No need of branded PSU if its only for HD 5670.I have Saphire HD 5670 and my PSU is zebronics 450W Sata Plus.Now i can play NFS Shift in 1600 X 900 @ 60 FPS.I havnt tried other new games.Assassins Creed also runs in 1600 X 900 @ 60 FPS
P.S My board is HT1 @1000Mhz having PCIe 1.0