PC Power & Cooling..
They have some really great PSUs..
and carry a full line..choices for the DELL PCs..
I chose a SILENCER 470..for a D915GAGL Intel BOXED Motherboard..
500-watts MAX..continuous power ratings..it fit perfectly into a DELL Dimension TOWER assy.
If you ever want to know who makes the particular power supply you have or are looking at buying, this is an interesting chart that took great time and effort to compile: