Sorry Rubick, but you are wrong!
The Mix Plus charges via USB-C just fine.
The biggest problem is finding an adequate charger that supports higher voltages then 5V.
I just did a quick search and the 29W apple charger should have an output of 14.5V x 2.0A.
If these specs are correct it will just charge fine.
Personally I use this charger for my Mix plus and it charges all the way: https://www.amazon.de/gp/product/B01KYXU3A4/