When do you get the flickering, just sitting in windows, when watching movies, gaming, benchmarking etc?
For example, my new computer is using 126W(at the wall) right now, and im reading the forums, while running Everquest2's patch program. My Seasonic PSU is around 80% efficient, so the computer parts are drawing around 100W from the PSU.
Running Everquest2, fullscreen @1920x1200 the power at the wall increases to 175W. Nvidia 7000 series graphics cards seem to be a lot more power efficient than the 6000 series.
Compared to my old 3.2Ghz Pentium Northwood + Geforce 6800GT, which ran at 145W Idle, and 230W while gaming.
Shuttle PSU's are pretty high quality, and im pretty sure it should handle the graphics card. If you were overclocking CPU/GPU considerably then mebee you would need more power, but I doubt its a PSU issue to be honest.
System Spec
Core 2 Duo 'E6700'
@stock 2.67Ghz
Nvidia 7900GTO 512meg
2Gig DDR2 @667Mhz
Seagate 7200.10 320Gig hard drive
1 Optical drive, 1 Floppy, 1 Zip drive
Soundblaster X-Fi
4 LED case fans