EVGA says that total power draw from a single card is 250W, but I have seen as high as 600W from my single card when using a modded BIOS and overclocked.......and this is *just* from the card, and doesn't take into consideration the power that the rest of the system needs. I have a 1200W power supply, and have seen total system power draw as high as 900W. Now, again, this is water cooled and with a modded BIOS which unlocks the power. If you plan on running on air and/or with a stock BIOS, you won't see anywhere near the power draw I am. So, to answer your question, depending on overclocking and BIOS, you could see anywhere from 500W to 1200W from two K|NGP|NS in SLI.

Thank you. I was thinking of getting a EVGA supernova 1000 p2 but i might get something a bit higher. And i was also going to do alot of overclocking on my cpu and the gpu's
 This is going to be my first build
Intel core i-7 4820k
EVGA x79 dark
2 x 8GB corsair vengeance pro 1866 MHz
2x EVGA 780 ti classified K|ngP|n edition
EVGA Supernova 1000 p2
Intel 730 240GB SSD
WD VelociRaptor 1TB HDD
Corsair 100i
 
And all that stuffed in a NZXT Phantom 820
 
 

Yeah i was actually thinking of going with that 1300

I tried to make sure a couple of years ago to plan for the future so i have a 1200 watt PSU

I am running a rampage iv black, 3960x, 32gb ram, 4 ssd's, 2 mechanical 4tb hd's, 2 kingpins, water pump and 8 corsair fans all running on a ax1200i. According to the I link software it never goes over 1000watts total usage.

Yeah, just like vsg28 said, it all depends on how hard you push your card(s). With an unlocked BIOS, and a voltage tool, you can really crank up the power going into these cards.