Will i be able to add another hd6950 1gb?

Sorry i doubt you can run it on a 620 it said on new eggs calculator you need a 800w PSU.

Sorry for the bad news  

found a good corsair PSU

http://www.newegg.com/Product/Product.aspx?Item=N82E168...

thanks for the input   i guess i wont be able to crossfire then hehe...

of course add the 2nd graphics card but make sure your psu can handle both

you can go xfire 6950 with upgrade from 620W to upgrade to hx/ax corsair 750W or above

take it my suggestion is wrong  

Both the systems used in the reviews below were Nehalems, so more power hungry than the i5 you have.
http://www.anandtech.com/show/4061/amds-radeon-hd-6970-...
http://www.legitreviews.com/article/1488/18/
They show maximum power consumption between 479-509W. The Legit numbers were taken from the wall, this is likely true for the Anandtech review as well, but I haven't seen it explicitly stated anywhere.
If they are taken from the wall then 10-20% can be taken off to get their actual system power draw and I think that is good number to use as a worst case for you.
A 460W load would only stress a 620W PSU to 75%. So it is within the capabilities of a 620W PSU to power a build with two 6950s. However no 620W unit I know has four PCIe connectors, so you would have to use adapters.