Bad Power Supplies

I just had a month old 550w power supply die on me, and it replaced a 350w power supply that died.  I now have a 420w power supply, but should I be concerned?  What is it causing my power supplies to fail?

Could be poor mains supply - frequent spikes, over-voltages, etc. can potentially be harmful to your PSU. Consider getting a decent surge protector, and maybe having your mains checked out by an electrician.