WuHT
Premium Moderator
First of all the 350 watt power supply does not fit the minimum for GTX 680 which requires a recommended power supply of at least 500+ watts (and the right kind with the correct power connectors - which most modern power supplies should have).
To expand on skytoast's post:
Better to err on the side of caution and consider springing for more wattage (500 being the minimum) and look for something 700W+.
Some board partners for the GTX 680 may have different power pin configurations, so make sure you look that up and save yourself some headache down the road (6+6 vs 6+8 pin)
Knowing the exact mobo will help a ton as well, which is more informative than giving the brand of the prebuilt PC.
If you're going to hunt around for best prices, you could consider those computer part pricing sites or try a computer building forum (which there are tons around).
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Guess my urge and natural tendency to assist others has overcome my common sense of generally ignoring whatever garbage ishimaru has to say.