Mine with a small 5v fan have temp beetwen 50-65c, I believe that it's just a coincidence that temperatures change with different power supply, but a few others test would be interesting. Anyway using the micro usb connector is not advisable, that pcb tracks are so small and the voltage drop drawing 2A maybe significantly.
Update:
It stop working, no led turn on and the cpu have a small blob on it. Very disappointed, evidently it cannot work out the box without an adequate heatsink.