Just make sure it has 2 6-pin PCI-e connectors, which it should at 650w. I'd definitely recommend investing a few dozen extra dollars (or other currency if you're outside the US) to get a quality PSU. As far as the wattage you're fine- requires a 550w PSU, which usually has you covered pretty well. Now, if you're using an inexpensive, crap-brand PSU all bets are off.
Here are the gereral features of my PSU.
# 650-watts total power
# 14 cm/5.51-inches fan
# One (1) 12-inch 20+4-pin ATX power connector
# One (1) 12-inch 4-pin 12V power connector
# One (1) 6-pin PCI Express power connector
# Six (6) large Molex 4-pin power connectors
# One (1) small floppy power connector
# Two (2) SATA power connectors
# Complies with ATX 12V 2.0 connector
# Short circuit and over voltage protection
I see it says 1 6-pin PCI Express Power connector.
Does this absolutely mean it won't be compatible.