[Nexus 6P Accessories] Elnrik:
Don't confuse USB 2.0/3.x with charging capabilities of type c cables and chargers. Consider that to simply be data transmission speeds.

Ok, so, I'll try to explain it. When you plug a cable into a charger, then plug the cable into your 6p, you complete an electrical circuit. (Obviously). Your phone is placing a load on the electrical circuit to run the phone and charge the battery. A better way to look at it is this: The charger is NOT pushing electricity to the phone, the phone is drawing power from the charger.

When the circuit is made, 500 to 900mA (legacy USB current) is drawn initially until the phone can figure out what it is connected to. It checks the cable to see what it is, where a resistor is supposed to identify ANY legacy connection type (read: anything that is not a Type C connection on both ends) appropriately. It sees the correct resistor identifying a Type A port is involved, it talks through the cable to the charger over the two USB 2.0 wires, and negotiates current using the BC 2.1 protocol exactly how much current it can safely pull. After talking to the charger, it sees it can pull 1.5A, so it opens up to that maximum amount and pulls what it needs to charge.

That's where the issue is. Manufacturers are marking the cables as 3.0A, so the phone just opens wide and pulls all it can. The charger's max rating is grossly exceeded, and the potential for damage can occur. I'm not sure what will happen to my 6p when the charger starts to melt, and I don't want to find out.

So, in this case, a Type A to Type C cable labeled by the manufacturer as USB 2.0 / 2.4A capable is accurately describing a cable that matches the maximum capabilities of a Type A USB *PORT*. That is a safe type a cable to use, so saying "stay away from the 2.0 cables" is incorrect. Right now, those are the ones you probably want!

Now, according to the Google Engineer (sorry I forgot your name already) and all the official specification documents I've read, 2.4A is the most a Type A port can ever provide, ever... Period... End of story. And it also seems that the 6p will report anything over about 2000mA (2.0A) as fast charging. So, this in itself is also causing confusion, because people see fast charging on their phone screens and automatically assume they are getting full charging speeds from a Type A port. They aren't. The 3A provided by the Type-C to Type-C OEM charger is the fastest you are going to get ...until other makers produce similar equipment.

Another mistake I see a lot is people making is reading the output rating of a car charger which has TWO ports, and thinking 3A output is enough for my 3A phone! Well... That's the max total DC output of the charger, NOT what each port is rated to provide. Cut it in half. 1.5A per port. Surprise!

Anyway... My suggestion, for now, is to wait until a Type C wall/car charger hits the market which is rated to output exactly 5V/3A on each port, buy a quality Type-C to Type-C USB 3.1 rated cable, and use that exclusively where you want to charge. Avoid Type-A ports like they are the plague until safe cables can be identified and purchased. A tip for you as well: the USB 2.0 rated C to C cables can be made longer (2.2m I think) than the USB 3.1 cables.

See also: http://xdaforums.com/nexus-6p/general/usb-type-c-vs-usb-3-0-3-1-vs-usb-2-0-t3221676

Hope that helps.