I use an old power supply(from a laptop,lcd panel, etc)...its rated at 13v DC 1.2amp. I even tested with one that has less amps and it works. As long as you dont crank up the audio you are using nominal amps so any 12vdc supply with 750ma or more will work. If you use a supply that doesnt have enough power the unit will warn you that your battery is low and will attempt a shutdown.
The power supply in the infill is made to run off of varying voltage/amp due to the fluctuations in a car so you dont have to worry too much. Just don't go over 14vdc for your test power supply and you should be good.
Dont waste your money on a sofisticated power supply unless you have other use for it.