C&P from www.advicenators.com
1. I'd make 100% sure the old supply is indeed bad; I'd try installing it in another case and see whats up if you can. If its another problem (loose wiring/connection for example), you might just be replacing supplies whenever a connection/socket/whatever goes 'wonky'. Kind of like a hot-socket. If you kept the old supplies (long shot I know) I'd try them as well, to make sure they dont work just fine in another case with different wiring, etc.
2. Hopefully you are buying quality supplies. If you are, it is indeed unusual to have this keep happening. I would call the manufacturers of the supplies and pick their brains. If it is something integral to your system (bad cooling, bad position in case, etc) I would think they might be able to point you in the right direction. I'd also be suspicious of the supplies being a problem, if you havent noticed either excessive heat or obvious damage to the supplies (or the particular smell, you'd likely know it if you smelled it).
3. I had the power button go out in a cheap system I had. If you are electrically inclined you can look at it yourself. That, or call the manufacturer of your system and have them help you troubleshoot so hopefully you dont buy a 4th supply if that isnt the problem.
4. Do you have problems with other appliances? Lighting problems? There of course can be external causes too, whether in your house wiring or in the power supplied to your house. As an electrician, I've seen everything from outlet problems (loose/broken/miswired/old/melted) to the wiring itself, and rarely there has been suspected voltage supply problems to the house. If you live in an old house, or an apartment this could be the problem, but thats only a guess. You could try calling your power company and asking if there is any problems but I've only ever gotten denials myself. If there is an intermittent power problem often no one can troubleshoot unless they get lucky and catch it happening ("Looks fine to me" syndrome). You can buy testers for duplex receptacles (like at home depot) that when you plug them into an oulet, they will simply tell you if there is a ground or other problem w/o having to know really what your doing (though you can do this with a multimeter/wiggy if you are experienced). Check to see if the outlet is loose or cracked, replace (or tighten) it if it is.
5. Get a surge protector if you want. Get guality, the ones you get from walmart/target/etc ARE NOT. They are simply glorified outlet extensions, and when they fail, they fail open - they arent usually designed to break the cicuit. I've seen these in houses that have been struck by lightening twice, and everything they were supposed to protect blew out. They just melted. If money isnt an issue, get an electrician to come out. They can look at the circuit to see if there is anything obviously wrong, and either install a surge breaker or a smaller panel to protect multiple circuits. I know Eaton/Cutler-Hammer has surge breakers, but who knows what you have in you basement (or wherever lol).