Power Supply

It states to only use the power adapter that came with. (9v 500ma)
Is it ok to use this with something like a pedal power box
eg (http://www.voodoolab.com/pedalpower_4x4.htm)

It has a 9v 400ma output.

Can this be used?

Your BeatBuddy will never be damaged if the voltage is matched (9v).
Your BeatBuddy simply won’t turn on if the polarity is unmatched.
BeatBuddy needs peek current at times, so having 400ma would probably be okay, but you may encounter situations where your BeatBuddy reboots but then proceeds to working as normal.