I have always had good luck just finding a PSU at Best Buy, which generally fit and worked fine. I got a recommendation for a new PSU for the above computer, which I purchased off the Internet. Suffice it to say, it wasn't even close to fitting.
I am looking for something in the 400 watt range, possibly a Seasonic or Antec. It really doesn't matter if you think it is good quality and will be compatible with the case.