Is it possible for these gou to Sli?

Solution
If they have the same amount of vram it will work Here is Guru3D's power supply recommendation:

GeForce GTX 680 - On your average system the card requires you to have a 550 Watt power supply unit.
GeForce GTX 680 SLI - On your average system the cards require you to have a 750 Watt power supply unit as minimum.

If you are going to overclock GPU or processor, then we do recommend you purchase something with some more stamina. http://www.guru3d.com/articles_pages/geforce_gtx_680_review,9.html
If they have the same amount of vram it will work Here is Guru3D's power supply recommendation:

GeForce GTX 680 - On your average system the card requires you to have a 550 Watt power supply unit.
GeForce GTX 680 SLI - On your average system the cards require you to have a 750 Watt power supply unit as minimum.

If you are going to overclock GPU or processor, then we do recommend you purchase something with some more stamina. http://www.guru3d.com/articles_pages/geforce_gtx_680_review,9.html
 
Solution