Dell Inspiron 531...bad PSU. What to replace it with?

Well, it seems the plugs are not proprietary (24pin and 4 pin), but I was wondering if a Corsair 400CX would fit in the case and do the job... It looks standard but......looking for someone that may know for a fact.

Yeah, the tower Dells (i.e, not the slimlines) generally use standard power supplies, and have for quite some time. The only exceptions I know of are some of the high-end XPSes a couple years ago, which used server type supplies. A few of the BTX ones are slightly taller than an ATX PSU, but the mounting holes and everything are the same, so you can replace 'em with a regular off-the-shelf ATX unit.

Good news... a 400CX is already on its way as a replacement...