The Dimension 4400 is not one of the Dell models that used the proprietary power supply, so any ATX PSU will do. Get an ATX2 model (most will be now), they are backwards compatible, and will have all the right connectors for any upgrades in future.
The Thermaltake right at the top looks like a good deal:
http://www.newegg.com/ProductSort/Su...SubCategory=58
