I had a budget gaming pc built for me back in March this year.
At the end of April, My PSU blew and had to be replaced (Evo Labs Pentium 4 600w) it was replaced with the same model.
Christmas Eve, It literally POPPED again. The bloke who built and replaced it last time has now coincidentally disappeared and no longer builds PC's....
My specs are as follows: Intel Q6600 2.4GHz Quad Core Processor
IP35 Pro Socket 775 Motherboard (Crossfire Ready)
4GB HyperX DD2 1066 Ram (2 Slots empty for upgrade)
Large Coolermaster CPU Cooler (Blue LED's)
4 x 120mm Coolermaster Case Fans and 40mm Chipset Fan
500GB SATA Hard Drive
DVD Dual Layer rewriter
650W Power Supply
Palit Sonic GTX 260 216SP Version Graphics card with HDMI, VGA and DVI Outputs (216 cores and 55nm version, boxed)
Aerocool PowerWatch Fan Controller and System Monitoring Display with Memory Card Reader
P35 express chipset
I suspect your psu was a cheap one.
Your graphics card is older and power hungry.
In your pc, you will want a decent 500w psu.
The corsair cx600 would be ok, and is the appropriate size.
It is a tier 3 unit on this list; you could shop for a tier 2 unit: http://www.eggxpert.com/forums/thread/323050.aspx
nVidia says minimum 500W for a PC with a GTX 260. 600W should be enough. I guess you just had bad luck getting two bad PSUs in a row. But you also had good luck because the PSUs didn't ruin the MB or other parts when they died.
I'm not too sure if they have ruined any other components ... There were 2 pops when it went on xmas eve, but even though it had blown my MB was still showing lights (it shows a digital 99) which Is what it showed last time when it first popped. I suppose I'm just going to have to buy a new PSU and hope and pray everything is okay.