I have a Dell Optiplex 360 with a Core 2 Duo E7400, with PCI Express x16 (1.0) and a 320w PSU I am planning on buying the ATI Radeon HD 5770 and the wattage calculators I've used have said I need about a 301W PSU to power my rig. I have 2 sticks of DDR2 800Mhz RAM (2GB total at the moment, but soon to be 4) one DVD R/W combo drive, 2 SATA 7200RPM HDDs, one 120mm fan, and a Sound Blaster X-fi limited edition (PCI). I set the capacitor aging to about 25% because the PSU I upgraded to is a few years old. Will this rig work? How will this card perform at PCI Express x16 1.0? And how much of an upgrade is this from an 8600GT? (Probably an obvious question but I'm just checking) And I am running Windows 7 Ultimate 64-bit.
It should, but you need to take into account that bad Power Supplies got lower efficiency. IMHO, you are playing with fire a little. You should invest in a good 550W power supply. You can find one for around 50$.