If I were you I would go for a 750W+ PSU to insure coverage for the future, like maybe you want GPU's in crossfire.
Get one with good specs
Such as a Single 12V rail
And go for a good brand such as "Corsair" as they have very good stability and efficiency
Getting more than 600 watts would be a waste for you. You will only need more than 600 watts for builds with two or more graphic cards for SLI (Nvidia) or Crossfire (AMD). However, a CF motherboard is also required and your motherboard doesn't support CF. Edit: As long as the power supply has enough wattage, enough amperage on the +12V rail(s) and is a quality one, you'll be fine.
As for compatibility. There are standard connections for all PC components, one for the motherboard, one for the CPU and so on. The only time you would need to worry about connections is again based on the number of graphic cards or an unnecessary number of hard drives or fans. For graphic cards, they use PCI 6 pin or 8 pin connections. The 7970 uses either a two PCI connections that being either a 6 and a 8 pin or two 8 pins. The power supply I provided will work.