The Thermaltake TR2 750w power supply is complete trash to the point of being dangerous to your other components.
TR2 and TR2RX are both tier 5.....basically do not buy under any circumstances.http://www.eggxpert.com/forums/thread/323050.aspx
The Extremegear brand power supply was likely a much better unit than the TR2. I would replace it ASAP. The brands you can count on are Corsair, Seasonic, PC Power and Cooling, XFX, Silverstone, Enermax, OCZ and Antec. Kingwin can also probably be added to that list.
For a single HD 7970 550w unit is sufficient. To run 2 x HD 7970s in Crossfire an 800w unit is recommended.http://www.realhardtechx.com/index_archivos/Page362.htm