It's very temping to screenshot this question and add a 'fail' stamp onto it.
Power supplies don't only work for a single socket. The variables that make the difference are the components used.
If you've got a 8 year old motherboard, you only need a 20 pin power lead to your motherboard, if you're board is only a few years old you'll need a 20+4 pin connection. One or two years old would normally need a 20+4 and 4 pin connection and some of the latest boards need 20+4 and 8pin connection.
If you plan on having a SLI setup, you need a power supply that will produce enough power and also have the right amount of leads needed to plug into your GPUs.
For an average system, 500W is fine.
For a gamer system, around 750W is fine.
For an enthusiast or anyone who has too much money a nice 1000+W supply will be fine.
Just remember to get a PSU that will cover your computers power needs, as well as cable needs. That's all there is to it.