Issues with 9600GT

[nelo]

My graphic card is a 9600GT (BFG) 512MB. Tested it on many games, it works ok... But on weaker games such as Team Fortress 2, and sometimes on stronger games like fallout 3. I'll notice my FPS spike, I dont think its just the spike, the Base FPS is really low. On fallout with most specs maxed I'll get like 20-10 fps. With no graphics maxed at all I get about 60-50.. During Call Of duty 4 as well, I won't be able to play for the first 2 minutes from my FPS spiking from 100+ to 20. I was under the impression it may be my PSU.

Manufacturer: Dell Inc.
Processor: Intel(R) Pentium(R) D CPU 2.80GHz (2 CPUs)
Memory: 3070MB RAM
Hard Drive: 320 GB
Video Card: NVIDIA GeForce 9600 GT
Monitor: Plug and Play Monitor
Sound Card: Sound Blaster Live! 24-bit
Speakers/Headphones:
Keyboard: USB Root Hub
Mouse: USB Root Hub
Mouse Surface:
Operating System: Windows XP Home Edition (5.1, Build 2600) Service Pack 3 (2600.xpsp_sp3_gdr.090206-1234)
Motherboard:
Computer Case:

There's my computer specs, my PSU is a dynex( I know the brand is ***...) 550w power supply. I was wondering what might be causing this, my drivers are all upto date. Help would be appriciated, thanks for your time

http://www.futureshop.ca/catalog/pro... 072461&catid [...] 2461&catid ( Link to PSU)

On my Graphic card box it says. "425W PCI express PSU combined 12V current rating of 28A or more" Is my PSU the problem, or could it be my CPU?