I wouldn't trust a $15 PSU. I found some specs. And what's this mean:
"Shielded Tube to Reduce EMI"??? Tube?
Output Range Noise Killer
Voltage +3.3V +5.0V +12V1 +12V2 -5V -12V 5Vsb Yes
Max Load 30A 35A 14A 14A 1.0A 1.5A 2.5A
Total Output 170W 200W 5.0W 18W 12.5W
Max Peak Power 530W to 560W
Uh, no. Those numbers add up to 405.5W, not 530W, although they are saying "Max PEAK." I wouldn't trust it. 14A on each +12V rail is probably not enough either.
Did you check the Dell's pinout to make sure it is standard? The size may be the same, but is the wiring?