Ah, the nerd might be correct.
"**Special Note to Owners of Dell Computers:** If your Dell computer was manufactured after August 1998, it may require the use of a proprietary Dell power supply. Although the Dell power supply looks like a standard ATX, it is a non-standard PSU that cannot be replaced with a standard power supply alone. Because of this design difference your Dell Power Supply may need a Dell to ATX power supply converter in order to be replaced with any of our standard ATX Quiet Power Supplies.
More information on Dell power supply conversion:
http://www.endpcnoise.com/cgi-bin/e/dellconverter.html