Model: Dell Inc. Studio 540
Operating System: Windows Vista
Processor: Intel(R) core(TM)2 quad CPU Q6600 @2.40GHz (4CPUs)
GPU: ATI Radeon HD 3600 series
Hard Drive: 623GB
Sound Card: Speakers (Realtek High Definition Audio)
Motherboard: Dell Inc. 0M017G ( http://www.findlaptopdriver.com/dell-0m017g-specs/ )
PSU: 350 Watt DC Power Supply
Your entire rig won't even consume anywhere CLOSE to 750w, so in this case, the lower the wattage, the better. Plus, the Seasonic PSU listed there is VERY VERY high quality, built BY Seasonic! Not to mention it's 80+ GOLD efficiency.
One last thing -coughs- I absolutely hate how the HAF series looks like, so that's a turn off right then and there
But in all honesty, you don't even need a 650w PSU, something like a 450w or 550w would suffice unless you're planning to add a beefier GPU in the future.