Best way to increase the lifespan of a power supply:
1) NEVER get the cheap crap made in china. Always get a reputable brand, like Corsair, Antec, Thermaltek, Seasonic or a few others. If it costs less than $50 (for a modern 750W or more PSU), then it's most likely crap. I paid my "Antec TruPower New 750W" PSU 140 Euros (approx. $160), but you can get 750W Corsair ones for significantly cheaper. Not only the "cheap crap" will last less, but it also puts your other components at risk if it burns. At least, even if you manage to burn your Corsair, it won't burn your whole motherboards before dying.
2) Do yourself a favor, buy yourself an UPS (uninterruptible power supply, not the delivery company

). Is will not only protect your PSU from the variations of the current in your area, but also save you from losing all your data if you have a blackout.
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SWTOR: 50 Jedi Shadow (Tank), 50 Sith Marauder (Annihilation).
LOTRO: Lifetime account, playing very casually.
WoW: Both accounts canceled for now.
GW2: Future Warrior.