So you mean playing a game/doing anything else power-hungry while charging the device? While that's at no time the best way to handle a rechargeable battery as it gets quite hot, it is, if you really want to do that, a question of power input versus output. As these devices pretty much all charge via USB (right?), the input is determined by the USB specifications, which are 5V voltage, 0,5A current -> 2,5W of energy. Often, USB devices specifically for charging have a higher curren, the maximum I've seen was 5A, but you shouldn't expect a lot more than 1A in transportation, maybe even just 0,5A (which is btw what most laptops give you, and the Pandora afaik too).Actually I was wondering if it would be possible to charge the tablets with atom x5 or x7 through USB port available in car or flights, because it's the kind of place you like to enjoy to use your gaming handled.
I think it would be possible to charge the pyra in this kind of USB port and play with it at the same time.
The output is even more unclear, as you need to factor in display brightness, CPU usage, memory usage, WLAN, Bluetooth and a lot more. The GPD WIN will probably do better than any tablet with the same CPU (as the big displays eat up a lot of energy while the keyboard doesn't), but it's impossible to say how good or bad any device does until it's tested. Even the Pyra will probably have problems playing some high-end games/emulator while charging, but then again, its battery is huge. I'll personally be happy if I can play Heroes 3 VCMI for 10 hours on the Pyra while it's on a charger