What they said. Here is a good power supply that can run a few 720i chargers:
http://www.rcgroups.com/forums/showthread.php?t=1051873
I have 2 of them (1 as a backup, or run both if I feel like using the full 860 watts of charger power I have - 4 hyperion chargers).
I actually bought 1 from him, and got the other off ebay for 22 bucks. You do need to jumper 2 of the pins to get it to produce 12v, but that is pretty easy to do.