I got it from dell. From their website I was redirected to startech.com. "ATX12V 2.01 power supply for dell pc's" 400 watts. The old one was 250 watts. I am looking at the box of the new one - and where it says "compatible dell systems: dimension series models" - there is no 8400 - which is what I have. Could this be a/the problem? I just noticed that.