You need to determine how much current the GB draws. The best way to determine that is to just check what the wall wart that came with the GB was rated at. As long as you provide that much current in whatever solution you choose, you should be fine.
Without checking, you will likely burn up the LEDWiz if you try to run the GB from it's power out. You should be ok with a PC power supply, but you really should check the requirements.