[HTC 10 Questions & Answers] lagittaja:
More accurately, the resistor tells the USB-C device that it's hooked up to a legacy "device". Type C to anything being legacy. Anything but type C weren't "designed to handle" 3A of current that the USB Power Delivery can output at 5V.

So if you have a Nexus 6P or a Pixel or whatever that uses USB PD:

if you use a type C to type A cable with a 56kOhm resistor, the phone is going to know that this is a legacy device and it won't attempt to draw more than the "Default USB Power" which is 5V0.5A for USB 1.0/2.0 and 5V0.9A for USB 3.x.

But of course the device will also look past it and see what output current the charger actually advertises it is capable of and then charges at that current the charger is capable of..

But, here's the big problem.

What if you use a type C to type A cable with a 10kOhm or 22kOhm resistor?

That cable is going to tell the device that it's

a) not connected to a legacy device (56kOhm resistor would mean legacy)

b) it IS connected to 5V3A or 5V1.5A (10kOhm/22kOhm resistor respectively) output.

It's going to try and draw 3A of current if the cable has a 10kOhm resistor in there, whether or not the charger can actually output that.

Danger here is that different chargers will respond to that differently.

The charger can either fail spectacularly (read: explode, catch on fire, something bad) or it will just trigger OCP (over current) and not charge if it has the protection or it will just try and cope with it delivering as much current as it can and potentially overheat and fail in some fashion.

Imagine hooking up your Nexus 6P or Pixel to your laptop with a "bad" type C to type A cable.. Those ports are not going to be able to handle that kind of power unless they're something special sauce.

For a little bit more cohesive explanation, read this

http://www.androidauthority.com/usb-type-c-and-3-1-explained-656552/

As for our device, we don't use USB PD. Some have said that the HTC 10 is compliant with it but I don't know if that's true or not.

However we use Quick Charge. Quick Charge doesn't look for resistors, it looks for the other chip inside the charger and talks with that chip, essentially doing a digital handshake before they initiate quick charging.

That prevents the charger from outputting anything higher than 5V unless the device specifically asks for it.

So, in theory, ANY data cable should be perfectly compatible with QC.

Data cable meaning that the D+ and D-, teh data, connectors are hooked up.

QC performs the digital handshake, and subsequent voltage/current adjustments, by talking across the D+ and D- conductors.

If you have a "charge only" cable or a PortaPow "data block" adapter, it means that only the V+ and V- connectors are hooked up and as a result QC chip in your 10 can't talk to the charger to negotiate the QC.

As for why some type C to type A cables don't support quick charge. I have no freaking idea.

I've got one cheap C-A USB 3.0 cable that I bought from ebay and it's a weird cable...

First time I tried charging it was in the car with a dual port (A) QC3.0 charger. Phone said slow charge, for faster results use the original charger. Didn't try again.

With the stock charger I'm testing at the moment, I first got 1.8A (after 1A>1.3A>1.8A over a minute). Unplug and plug it the other way around I got 1.7A and then it dropped to 1.4A. Third time I plugged it in the same way I plugged it the first time and now it said slow charge.. Plug it again the same way and now it charges.

Could it be that the cable either has a 10kOhm or a 22kOhm resistor in there? Maybe. Idk. Don't have means to test it right now, but I'll probably gut the cable later and measure it when I have time.

Moral of the story: come on guys, buy good quality cables from reliable brands for charging. They're not expensive.. Aukey, Anker, PortaPow, you name it. There's a lot of them out there.

I'm personally using the PortaPow cable for charging my 10, only 1 meter length available at this moment but if you want longer or shorter lengths, message them. They'll make them if there's enough interest.

http://www.portablepowersupplies.co.uk/portapow-charge-sync-usb-c-cable/