EVGA 500 W1, 80+ 500W Power Supply

I have a Dell XPS 420 that I got new back in 2008. Since then have added a better video card, wifi card, additional dvd/cd reader burner. The unit came with a 375 Watt power supply, but since I added the bigger video card and other items I thought for the price maybe the EVGA 500 W1, would let the computer run a little easier. Was told it would fit my Dell and for 40 bucks how much can I lose. Well the four mounting screw holes do not match the Dell screw hole and the only way to get it mounted is to turn it upside down with the fan up, also the power plug can not be installed due to the case design and for both reasons that is why I had to mount it with fan up, and so the power cord could be plugged into it.The mounting screws luckily aligned at three points not four, so it is attached to the case firmly, but due to the size difference has a space on the one side of about a quarter inch. Removed a few items to clean dust and just try to run the wires in the same way the older unit did. Some small problems due to my error in mismatching plugs but just switched them and my Dell is running OK, for now. The wires are long enough and all that had to be used had enough length to them. Only problem, and this is why I only gave three stars is that the fan is on top with only about a little over a quarter of an inch clearance from the top of the case. Ran the computer for about two or so hours and played a couple games and did some other things to see how it worked. After turning it off I noticed the area around the power supply was warm, not excessively warm but then again I really never had checked the power area before to have a comparison to judge by.