The way I see it, Power droids are more than walking generators. They are also repair droids (they diagnose systems to find the causes for power outages etc.) Therefore I wouldn't roleplay a power droid any different than an R2 droid. He has built-in equipment, like a retractable arm, that interface thingy, and a holoprojector (to display his diagnosis to a repair crew.)
I've just read a great story hook on wookieepedia:
Allegedly a fringe group of power droids have set up a religious cult and want to proselityze/solicit funding. If your power droid plays the guru of said cult (or his second-in-command,) you could play a droid Entertainer with a couple of devoted fans among the droid (or even meatbag) community.