Third party power supply?
I've never had issues but my OEM power brick can get awfully worm...i would say hot after a session plugged in. Maybe fine but seems like it may be inefficient or the power draw is pushing the limit causing heat? No dock in use either.
What aftermarket power supplies are you using? Something rated a little higher...I know the Lego will only pull what it can but maybe some headroom will cause less heat at the brick.