I am struggling to understand USB type-C specifications in terms of power supply,

took me a lot to figure out about USB data bandwidth but now that type-C is used to charge

mobiles need to learn more.

Question seems simple to me, hope so. I need a fast charging USB adapter and looking

online I found out one that says super-speed and has a detachable USB type-A male to type-C male cable, nobody lists the tech specs clearly, but as far as I undestand a type-C to type-C cable could carry a lot of power, while a cable type-A male to type-c male could do less. So what is the max Volt/current/Wattage of USB cable type-A male to type-C male ?

This is a picture of what I call a USB cable type-A male to type-C male, just to be sure I am getting it right.enter image description here

I am editing the post because of the first answer and what it states:

so why I am getting this kind of specs for the usb charger with female type A plug ? reads 5V 9V or 12V :

enter image description here

  • The charger you added in your edit does not appear to be using the USB standard. It will not provide 9V or 12V to every device, it will provide only 5V unless the device is compatible with that charger. (I have no idea what devices are compatible with that charger, because 9V does not make sense for a standard USB Power Delivery 1.0 charger and USB power delivery 2.0 is for Type-C only.)
    – Romen
    Commented Jul 25, 2022 at 17:14

4 Answers 4


USB Type A is the limiting side of the cable. All of the USB Type-A and Type-B ports are standardized to operate on 5V and that means anything you could possibly plug that A to C cable in to for charging will deliver only 5V.

The other thing to consider is the amperage of the USB A port though.
An older USB 2.0 port on a PC is limited to 500 mA. A newer USB 3.0 port on a PC is usually limited to 900 mA too. Wall adapters and special USB ports that are meant for charging USB devices can offer more amperage. I have seen up to 3A over USB Type-A before but that is definitely outside of the USB spec and may be unsafe with some cables.

The maximum amount of power that the USB Standard allows over normal Type-A is 7.5W, which is 5V at 1.5A.

USB-C has much higher power throughput because the newer standards for this port use extra pins and the devices communicate with each other to negotiate a voltage that they both support. This allows the cable to use a higher voltage and deliver more power without getting to unsafe high current.

  • Hi @Romen thanks for your prompt answer, I edited my post because of your answer, see what the specs reads for the charger with usb type-A female plug and so my question about the cable, I am confused
    – pippo1980
    Commented Jul 25, 2022 at 16:52
  • 1
    Cables are just wires. If you want a technical answer about the cable alone then the max power any wire can handle has to do with how thick it is and its conductivity. USB is not thick and there are a huge range of cables of varying metals and quality so it's hard to give a safe "max" answer that is above 7.5W. 7.5W is the max wattage that all USB Type-A cables are officially supposed to handle.
    – Romen
    Commented Jul 25, 2022 at 17:12
  • @Romn so it works because uses an extra specs cable with non standard features ?
    – pippo1980
    Commented Jul 25, 2022 at 17:33
  • I don't understand what you want me to modify in my question. I am not saying that an "extra specs cable with non standard features" even exists. Every USB cable is meant to work with the USB standard and 7.5W is the maximum power that the devices will put over the cable. Changing the cable does not make the power go higher. If the devices have some non-standard power feature then you need to be specific about what brand or technology you're asking about. I am only talking about standard USB in my answer.
    – Romen
    Commented Jul 25, 2022 at 20:11
  • So probably I dindt get your answer right. You says USB type-A goes up to 7.5W. Is a male USB type-A to male USB type-C a type-A USB device or a type-C device ?? If the answer is: it's a type-A device so why a USB adapter outoputting 5v, 9V or 12V should work with it ?
    – pippo1980
    Commented Jul 25, 2022 at 20:34

max USB cable type-A male to type-c male Volt/current/Wattage possible?

  • you probably should not ask this question here, you're not going to get a good answer.
  • nature of the question is quite open, just saying possible. do you mean transmit data or do you just want to jump start a diesel engine? And you did not specify DC or AC or whether within any kind of [safety] specification.
  • google will quickly tell you Can all USB-C cables do 100W: All USB-C cables must be able to carry a minimum of 3A current (at 20V, 60W). But for high-power 20V/5A (100W) charging, you need a 5A-rated USB-C to USB-C cable that contains E-Marker chip to identify the cable and its current capabilities. Or a Thunderbolt 3 cable that supports 5A/20V (100W) charging.
  • in simple engineering terms, possible == before the cable melts and simply puts voltage/current to the other end no data transmission... the shorter the cable and the higher the voltage the less current which means less heat; I'd wager about 100vdc and 300w before things get squirly but that's just my opinion. Given the spec is 100w @ 20vdc I'd suspect fair headroom and 200w @ 40vdc on an 18" or less cable would work, how far above that you try it out and let us know when the cable melts. Cat5 PoE can do 100v, for reference.
  • https://www.cnet.com/tech/computing/usb-c-power-upgrade-means-240w-for-gaming-laptops-and-other-devices-in-2021/
  • According to worldwide agreed standard specifications.... in any case is a type-A to type-C a C standard cable ?? Wasnt able to get a google answer to that ? Thank you in advance for your time/help
    – pippo1980
    Commented Aug 3, 2022 at 19:40
  • 1
    you'd have to dive into "specifications" then see who's manufacturing what to what spec, and if you trust that. I don't know the details between USB 2.0, 3.0, 3.1, 3.2, 4.0 and the A, B, C connector end and the wiring in between. Fact is the size of the connector [pins] and wiring and quality of manufacture will dictate what max wattage/current/voltage is possible, not necessarily a "spec".
    – ron
    Commented Aug 3, 2022 at 20:12

Charging is quite simple. It depends on the maximum current in Amperes(Amps) that the cable can carry. The maximum Amps that any USB charge cable needs to carry is 5 Amps (5A). As long as it can carry truly carry this much current without overheating, and the wires are wired correctly on to the connectors you should be fine in any use scenario. The voltages don't matter and the wattages don't matter with regards to the charging cable. The only other thing to note with regards to unprotected cables without the emarker chips, resistors etc. are that as long as you are using the correct charger (for that particular device - does not have to be the original one, just one that is truly compatible with it-even third-party ones) it should work out fine.


as solved on https://electronics.stackexchange.com

by https://electronics.stackexchange.com/users/241749/macguffin

here: https://electronics.stackexchange.com/questions/628801/what-is-the-maximum-usb-cable-type-a-male-to-type-c-male-voltage-current-power-p

I am copying it:

They say it can deliver 5 V, 9 V, or 12V and I was trying to figure out how it would fit the USB standards, given that everybody everywhere says that USB 3.1 can output max 7,5 W (5 V at 1,5 A I believe). The adapter/charger carries an USB type-A female plug instead of a type-C which they told me could carry more power.

The short and simple answer is that they don't follow the USB standards.

The longer answer is that entities outside of the USB Implementers Forum (or USB-IF) wrote what might be described as "extensions" the USB standards that put more voltage and/or current into the USB-A connector than the USB-IF allow.

There's more than one of these extensions to the USB spec on power transfer, and not all of them are compatible with each other. Some require non-standard cables to connect a USB-A power brick to a USB-C device to charge at the higher power levels.

That gets back to the earlier question:

So what is the maximum voltage/current/power of a USB type-A male to type-C male cable?

The answer is it depends on which standard the cable follows.

The USB-IF has bumped up the maximum allowed current on USB-A over time and last I checked it allows a maximum of 2.4 amps. The voltage allowed on USB-A is 5 volts, at least according to USB-IF. There was the USB-PD 1.0 spec that allowed higher voltages on USB-A but I have not seen anyone actually use that spec in any devices available to the public. It appears the USB-IF decided that USB-PD 1.0 was a bad idea and will not even test if devices comply with that spec. USB-PD 2.0 replaced it, which was updated with USB-PD 3.0 and then again with USB-PD 3.1. USB-PD 2.0 and up defines power transfer for USB-C, leaving USB-A at 5 volts and 2.4 amps as defined in other specifications.

These specifications created outside the USB-IF are so numerous, and go by different names depending on who is selling it, that it is difficult to say where the maximums on voltage and current lie. Technically any connector that is rated for more than 5 volts and 2.4 amps is not a USB-A connector even if it looks like one. If you ask what is the maximum voltage and current allowed by the USB spec on a USB-A to USB-C cable then the answer is 5 volts and 2.4 amps. If the question is how much is allowed under standards outside what the USB-IF wrote then it's something like 20 volts and 5 amps.

How can these cables handle this much power if the USB-IF considers this much power unsafe? One "trick" I saw was using all four pins in the USB-A connector for power. This clearly violates the USB spec and renders the cable unusable for USB data transfer. To make this work the device being charged has to use some circuitry that is outside what USB-IF defined, or the cable has circuitry outside what USB-IF defined.

There's a long history on why these "high power" USB-A power bricks became popular, which I won't go into because of length. They are still popular today out of inertia, once they caught on it became difficult to be rid of them.

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