Cheap, low quality power supplies not only generally do not produce their rated voltage they also can produce high ripple and noise on the individal rails that can actually damage your components. They also tend to fail, sometimes dramatically when stressed.
Aptiva is on the do not buy list.http://www.eggxpert.com/forums/thread/323050.aspx
I would not even trust a single GTX 680 to a piece of junk like that. A $500 graphics card deserves a quality power supply.