Very simple to charge your phone / tablet / 2nd display used for video. I use a samsung Note 8 (as it has one of the brightest NIT screens of any device for the money) and when I plug it in to the autel controller to fly, it begins charging. Actually I don't know how to disable this, so it should be very easy for you to charge your phone/tablet screen when flying.
If your tablet isn't charging, perhaps it needs higher voltage than a standard phone and can't charge off the remote control (for safety reasons it makes sense not to discharge the controller battery when flying so perhaps the current is limited ).
I know my ipad won't charge off AC power with standard USB-C charger, only the apple provided one works so I assume it's an issue related with higher current needed by tablets.