[Moto Z Play Questions & Answers] KrisM22:
Thanks for this. A close read of that indicates to me that there is going to be a ton of arguing over what is safe, and some burnt out 5v power rails in some, especially older, computers.

The mention of 56Kohm resister in cables has caused some cable sellers to advertise that, but having that, in and of itself, I believe doesn't do anything - you need load balancing circuitry in both the phone AND the charger to utilize it.

I read this quote with amusement "A good cable uses a deep-draw extrusion method that produces a Type C plug that is a single piece of metal and does not have a visible seam on one side of the plug,". My phone came with a factory Motorola hi speed charger that is rated for 5v 3a (15w), and it's C plug has just such a "bad" seam. So many people make such blanket statements that simply are not true.

I looked at one of my wall-wart chargers(this particular one is stamped Samsung) and it is rated at 5v, 0.7a (3.5w), so it's a good bet that if I plug my old A to micro to micro-to-C adapter to phone, that nothing bad will happen. Another one (Moto) rated at .8a. A 3rd one that came with my Moto G3 is rated .55a .

1)So if one goes to ebay and buys a wall wart rated at 5a and uses old cables and adapter to plug it to a Moto Z, what will happen? Dunno!

2) I have had my Moto z plugged very often to my computer with just such an arrangement and have not noticed any "fast charging".

I have a huge 850w PSU in my computer, but that does not mean that all that amperage available on the rail is permitted through the USB connection. Intel offers some ideas and I would bet that most current mobos have such limiting circuitry: I am sure older (than 10 yrs?) do not, or at least not as effective.

http://www.usb.org/developers/docs/whitepapers/power_delivery_motherboards.pdf

The phone also has smart limiting circuitry, but of course I don't know what it is.

Am I more in jeopardy with an old A to micro cable with C adapter, or a new A to C cable. Dunno. Certainly any wall wart should be from the/a phone mfgr, or rated below an amp or so. I don't know if you can make this phone fast charge for 30 min if it's rated for 3a, without an official charger. The remainder of the charge time is governed by the phone to be at a much slower rate.

With this new phone, I have yet to connect it to a wall wart other than for 5 min to the official one just to make sure it worked, and I don't recall any high speed message. It winds up getting a 100% charge just by being plugged into my computer since I am doing file transfers and the like.

As to the plugs themselves, you can run much more amperage through an A (few wide conductors) than a C (many very thin conductors).

A very great deal is being made of this one incident. It is hard for me to understand how a different cable can burn out a computer. You can run 10 amps through any cable (though it will get more than a tad warm!), but amps in a cable is not a problem. It's the governor, or lack thereof, in the source (wall wart or computer) and the target (phone or another computer). If the computer presents a short circuit to the cable, something will surely fry, but no device, these days, should ever do that.

A cable (they all are made in China, but there are many factorys there with widely varying QC), with an M stamp on it or not, is still just 4 wires in a sheath. If it is poorly made, or the connectors at the ends are poorly made or poorly attached, there will be trouble.

Okay, that's enough words for this post, but, for sure, this topic will be around forever!

EDIT: C type connectors have been in use on phones for years now. Why have we not heard of any phones destroyed???????