Interested to real about this on another website yesterday:
Particularity poignant for me as I had a messy mistake with USB-C at Xmas - I bought a USB-C to Micro USB cable so I could change my backup Nokia 5 and my wife's Kindle from my Macbook USB charger (which I use to charge my iPad and iPhone).
I plugged the Nokia in with it and left it for no more than 5 minutes but came back to find a smoking blob of plastic sticking our of the phone.
The cable was a reasonably well known brand (Anker) but it looks like there has been a short or arcing in the micro USB in the phone and the USB-C can deliver so much power it has toasted it.
The other thing I noticed is the end is a very loose fit at the USB-C end into the charger (and my Macbook) compared to the Apple ones