I think that is the one im going to get.
Can someone briefly explain the voltages to me in case they dont have this one in stock.
What should I ask/look for in a power supply around 800 watts?
That's a nice PSU. If they don't have that one, be sure to look for one from a known quality manufacturer. I already posted what I think you should look for in a quality PSU. I also posted some known quality manufacturer's.
There isn't a good way for a home user to test a PSU. The only way is to replace it with a quality unit from a known quality manufacturer like Corsair, PC Power & Cooling, Seasonic, Antec, etc...
The things to look for in a quality unit are active PFC (no little red voltage switch on the back of the PSU), at least 80 Plus certification, and more output on the 12v rail(s) than on the 5v and 3.3v rails.
The OCZ unit satisfies all these conditions. It has active PFC, is 80 Plus Gold certified (the best efficiency you can currently get), and puts out 71A on the 12v rail. It also has a 5-year warranty.