LatiosXT if you have a lot of bad luck with psus, you may want to check the line voltage in your house. It may be running less than 120 volts. This goes for the poster of this thread as well. All you need is a multimeter to check it, ten bucks at Radio Shack.
I've had this happen in three different places. So unless the entire city of San Diego has crappy power, I'm just going to point at the PSU.
EDIT: Well just to check, I ran my Kill A Watt around the house (I have a DMM from Radioshack, but I'm dubious about its voltage range), they were all 116-117V. Yes this is short of the 120V, but most automatic power supplies are rated for 100V-240V. So unless your entire house is below 100V+/- some percentage...
Besides, if the voltage was bad, then it wouldn't just work. Even if PSU's were purely analog (and not subject to voltage requirements), the computer (which does require some voltage) would just shut off right away. But PSUs have digital components in them.