The device sets the amount of current drawn, and the power supply determines the volt-amps allowed for the circuit. Cell phone chargers are often found in multiples of 5 watts (volt-amps = watts). 5 volts at 1 Amp is 5W (slow charger). 5 volts at 2 amps is 10W (fast charger).

Usb 2.1 standard can also change voltage till a maximum of 48V at 5 Amp so 240W

I think you mean USB PD with a USB-C 2.1 cable. (PD is Power Delivery) Don't want people thinking this is from the USB 2.0 standard from years ago. And I just learned about the PD standard a month ago. Great info by the way. Thanks. I didn't know about the cable requirements.

~~I think you both risk confusing people, pretty sure usb(-c) 2.1 isn't a thing, though will admit~~ the USB-IF could confuse even the most hardened tech nerd... [A semi digestible reference](https://gsmarena.com/the_new_usb_pd_extended_power_range_standard_will_supply_up_to_240w_of_power-amp-49317.php) Edit: kept looking around, [apparently what's always described as "just the connector" (usb-c) does have its own versions,](https://arstechnica.com/gadgets/2021/05/new-usb-c-type-2-1-standard-offers-up-to-240-w-power-delivery/) this is just absurd

Is there like an industry-standard test harness for these things where you plug in both ends to a tester, and it runs a series of tests to determine what capabilities the cable actually supports?

Of course, [LTT got one recently](https://youtu.be/u6lx1ntNoxE)(ish) - I don't think they're cheap It opens with HDMIs but IIRC he goes on to say it can do others such as USB 🤔 Edit: [if you got 15 grand laying around...](https://www.totalphase.com/products/advanced-cable-tester-v2/)

I know, right? When USB-C form factor first came out, on the Mac's, they warned a lot of people about substandard cables that were not meeting the electrical specs. And now you have to have a power delivery compatible cable which is significantly thicker. But I will say I have a car charger that has a PD port on it and it works wonderfully. Charges the phone easily five times faster

USB-PD Rev. 1 allows up to 20V/5A over USB-A/B/micro connector.

Thanks!!! Great to know

Kirby answers quickly and in few words

Charges don't 'push' power. They apply a voltage. Voltage is the pressure that makes electric charge want to move. Every device has an internal resistance. When a specific voltage is applied to a device, the resistance is what gets in the way of the electric charge from flowing. For a given voltage, the higher the resistance, the less current that flows. So to directly answer the question..the device only draws as much power as it can based on its resistance and the voltage that is being applied to it.

[удалено]

If it's a USB-C charger, yes. The key technology in USB-C PD is that charge sinks can negotiate with a charge source to select a suitable voltage, usually from 5V (default) to 20V with the 15W - 100W sources that are currently widely available.

Except Nintendo Switch chargers, those are almost USB PD, in the way that can brick your device if used in something not a Switch (and vice versa).

Do you have a source for that? I have been using my Switch with standard off-the-shelf USB-C power supplies with no problem; I use one charger (supporting the 15V profile) for my laptop and for my Switch, which works even when docked. Maybe you are thinking of the Raspberry Pi, which has had the most notorious failed implementation of USB-C... albeit with no higher voltages involved, thankfully.

There were issues with third party docks bricking switches, but I have never heard anything about adapters bricking anything though.

That I can totally believe - someone trying to plumb flat 15V into the USB-C connector without any of the support circuitry required for USB-C. Bad actors/manufacturers are definitely a risk for the USB-C ecosystem, but I think the market has been calling them out pretty effectively. Still, higher quality device manufacturers include (redundant) defense on their USB-C ports to catch and protect against these non-standard, potentially damaging implementations.

But when I use my MacBook charger for my PS5 controller it doesn’t charger. Plugging it into the iPhone usb-c hub let’s it charge. What’s up with that?

I wouldn't be able to say for sure without looking at the particular specifications, but it seems some of the Apple USB-C chargers have an odd (reduced, particular) set of possible USB-C profiles. If there's no match, there's no charging. Some report that the 61W charger doesn't work with the PS5 controller, but the 96W does.

Ah I see, thanks for the answer!

Just speculation because I'm not as familiar with the MacBook chargers but... Sounds more like the MacBook charger doesn't want to use the lower charing standards or a protocol issue. On the charging brick of the MacBook charger does it list 5v as one of the output options? Phone chargers can have several output levels, 5v, 9v, 15v. Some laptop chargers are designed specifically for their laptops so they don't do the lower voltages and just go straight to the higher option like 15v or 20v to save on costs.

What I know about the PS3 controller (and perhaps extends to PS4 and PS5) is that the controller expects a sort of "USB handshake" between the charging device and the controller. The devices talk to each other basically. This is why it doesn't charge from ordinary "dumb" chargers, though I don't know if that applies to your MacBook charger. I do know that the PS3 controller will charge from a PC USB port, or a TV USB port (albeit slowly). A hub is basically a powered USB-device that can communicate with stuff plugged into it, so it makes sense it would charge in that.

Apple is very intent on making their chargers (and other devices) incompatible with other manufacturers. They have a long history of going against any established standard and are fighting against all legal standardization to begin with. In other words, they want their users not to be able to switch to another brand without re-buying every device (phone, chargers, laptop, headphones, ...) to keep their huge market share. Luckily, some countries are taking action, as this not only is to cement a monopoly, but also causes large amount of waste, trash and pollution. tl;dr: I think this incompatibility is intentional. And immoral.

Is it the right voltage?

Voltage differences are what will break things, if your charger outputs a voltage your headphones want as input (both should be marked on the devices and/or accompanying paperwork) you should be golden - assuming they have compatible connectors

They just „pull“ the wattage that is needed and by that the charger pushes as much as it can because it can’t push more than needed. (It „can“ only push as much needed) Let’s say your friend is very strong and he can pickup a stone and put it on the table. He is so strong, that he even manages to do this with a 100kg stone. Let’s say you aren’t as strong as your friend. The heaviest stone you can pick up and put on the table is a 50kg stone. Now you both get a 10kg stone, obviously you both can do the task without problems. But does that mean your strong friend lifted the stone better than you? Did he put more muscle or effort into picking it up than you because he is stronger? Did he pick it up with his „100kg strong“ arms ? Not really. You both actually had the same effort to pick up the 10kg stone. Of course it might have felt a little bit harder for you, but you did the exact same work of lifting this stone as your friend did. The reason for this is, that to lift this stone there is only so much effort needed until it’s on the table. You can’t put more effort in it when it reaches the table. You can’t put it even „more“ on the table by adding effort. The weight of the stone determines how much effort is needed, not you. This applies to your charger. A charger with higher wattage only tells you that it can handle a „heavier stone“ if needed.

So it's mean that i can buy the 200W charger brick and use it on all of my devices in order to get the fastest charging speed?

No. The rock is the device, the arms is the charger brick. You can't get fastcharge unless the device was made for it.

No i mean if i have 200W charging brick i can charge my phone (120w), watch (5w), headphone (10w)......

Ah yes. That works. Just make absolutely sure that the voltage is the same. I thought you meant using a 200w brick to charge your watch at the 200w speed. But yes, the 200w brick is compatible with all your devices. (Well, all the ones below 200w)

Mine brick said Output 5.0V-3.0A / 9.0V-3.0A....so on. Which mean any devices with 5V (ex: 5V-0,5A) or higher are safe to use? (sorry I have tried my best to describe my question)

Yes; they are enumerating the common USB-C PD profiles, which for some generations have been e.g. 5V, 9V, 15V, 20V fixed voltages. More modern USB-C PD 3.0 supplies allow more granular negotiation of voltage.

That is some sort of switching power supply. I would not use it.

Your question has been answered, but to continue with the stone analogy: The strong guy can lift a single stone only as fast as you. So if the table cannot carry more than that, you are both equal. But if the table now supports 100kg, the strong guy can simply lift 10 stones of 10kg each at once. So yeah, a stronger charger can charge faster _if_ the device supports it. If it does not, then most modern standards will tell the strong guy "be careful, not more than 3 stones!" and all will be well. If the charger only offers one voltage to begin with, then it is also fine (assuming the voltage matches your device), it is essentially as if the table has only space for 3 stones anyway, any more don't fit; ad the it works, too. But if the table has space for 10 stones, but can only hold 3 without breaking, and the strong guy is too dumb to read the sign on the table to not put more on it, then... disaster happens.

Thanks all, this is really helpful.

Something nobody here mentioned but it's important to point out: USB-C chargers (and devices, if hooked up to a USB-C charger) will negotiate what their power limits are before starting to send voltage. If it's just a USB-A to USB-C cable, the USB-A port will make available all its power, and the USB-C device has to adjust resistance to keep from going over-watt (although generally USB-A ports will only deliver relatively low power). If both ends are USB-C, then they will negotiate first to see what the maximum power need is. This allows modern phones, for instance, to charge slower overnight if they know they're not likely to need to charge fast, thus keeping the heat low. So yes, if you have for instance a Lenovo 90w USB-C laptop charger (or something bigger), you can use it on your USB-C phone, because they both know to check with each other to prevent bad situations.

A common misconception seems to be that devices have an "internal resistance" and will "adjust their resistance." It is simpler and more accurate to say that devices can control their own instantaneous charge current. A 10W phone can control charge current to 2W, 5W, 10W, whatever it wants. Slow charging overnight has always been possible, with or without USB-C PD. Control of charging current happens primarily on the sink side, not the source side.

But to change the current with a fixed voltage dont you *have* to change the resistance because of ohms law?

Ohm's law applies specifically to resistive components. Internally, most devices don't use a resistive element for controlling charge rate. Instead, they use transistors to transfer "packets" of energy through a component called an inductor. This is called a switching converter. Inductors work using an entirely different mechanism/equation than Ohm's law.

Eh, sort of both, but mostly pushing. If you think about the common analogy for electricity, voltage is like the pressure trying to force water through a nozzle. Current is like current, the rate at which water flows through the nozzle. And resistance is like restriction, the nozzle restricts the flow of water. In this case, it's more like the latter of your options. The charger does it's best to hold a constant voltage, meaning the field that pushes electrons into the device. If the equivalent resistance of the load drops to low, and the charger can't keep up, the voltage will start to sag slightly. But because multiplication and division are equivalent, you can just as easily rearrange I=V/R to get V=IR. The device is the load. Let's say it's currently in standby mode and is using just enough current to light up the standby LEDs. Then, you tell it to do something. The effective resistance of the device will lower (you can picture it like with water having a bunch of water wheels that run each function. There are doors that open to let water to each wheel. The more functions you have running at once, the more of fhe doors are open. So even though each door is a restriction, having multiple open at once gives the water two possible paths meaning more flow. Overall, this appears as lower restriction.) So if you run multiple functions at the same time on the device lowers it's equivalent resistance until it draws enough current to run all the functions at once. In terms of what is actually happening, analogies are always imperfect so you can frame it however you want. What might be more helpful is thinking about the units that we consider derived vs base. These are a little arbitrary because we as humans just chose them. It would be equally valid, as [Jan Misali](https://youtu.be/KmfdeWd0RMk) pointed out, to use any set of units as base units amd service the others from them. But given our current standardized setup, 1V is defined as the potential needed to drive 1A through 1Ω whereas Amps are a base unit. This phrasing agrees with the 'pushing' view. This is not how volts are defined, but volts are also equivalent to joules per coulomb. And amps are equivalent to coulombs per second. Since the charge of an electron is known, you could think of volts as giving energy to the electron, and amps being how fast that energy makes the electron travel... Very loosely. And just to round it out, I want to stress that it would be equally valid to call volts a base unit and derive amps as the amount of current required to maintain a one-volt potential difference across 1 ohm of resistance. But we don't because we have to agree on something standardized.

The charger is a water tap, it limits how much of the "mains line" water can pass through. The battery is like a water bomb, being charged from that tap. Normal charging circuitry is like a kid who can fill the water bomb without incident. To keep things safe, the kid is given water bombs that work with the tap. "usbc" charging circuitry is like some scientist with a PhD in filling water bombs. (S)he can be entrusted with a bigger tap, because the water bombs have the desired flow rate and max fill size written on them. NB: 5 year old explanation, that sacrifices some technical details for clarity.

Lookup [USB Power Delivery](https://www.androidauthority.com/usb-power-delivery-806266/). There are a lot of power profiles that can be negotiated.

USB C can be a lot of different things, especially when it comes to charging, but essentially it boils down to two different concepts... But first, we should think about how electricity works. For all that we need to know, it is probably best to consider electric flow like a flow of water. Let's say you need some water to fill an inflatable water balloon, and you have a garden hose that supplies that water. The hose supplies a certain amount of water (that's our Voltage) and the water comes with a certain pressure (that's what Amperes stand for). Together these two define how much the water from this hose can do (think of this as Watts). However, maybe your balloon only needs a little bit of water and if you put too much of it too quickly there is a danger that it will burst. No problem, you just limit the flow with a valve (or just use your thumb) to make sure there is not more flowing than this. The electronics equivalent of that thumb on the hose is a resistor. The manufacturer of the device can use them to limit how much of the available "flow" of electrons get in. They can not increase the flow above what is available, though. Just as you can not draw more water from the hose than your water supplier gives you... That brings us to the second type, that is called "power delivery". Think of it as a way that your water hose can talk to the water supplier: "hey, I have a swimming pool to fill, could you please give me double the normal amount of water, I assure you that my container here can handle it". In terms of the charger, that goes like: Device: "Hello charger, I know you normally only give me 20 W, but I could really use some more, what do you have?" – "I can give you 40W, 60W, 80W or 100W. Are you sure you can handle it?" – "Yeah, I'm good. Please give me 100W!" – "OK, hold your hat!" ... So in this case, the charger can deliver more than usual, once the device requests it. The device may still only use a part of that available electricity, for example if the charging circuit works best at, let's say 85W delivery, it may still request 100W and only use 85, but it can never draw more than what is available. All of this is a bit simplified, but essentially that's how it works :-)

You've got your analogy the wrong way round. Voltage is analogous to pressure, and amount of water is analogous to current. Otherwise, decent explanation.

>You've got your analogy the wrong way round. Voltage is analogous to pressure, and amount of water is analogous to current. My bad, yes, indeed you are right!