Hey all, first post here
 
I was unsure if I should put this in the Power supply section but here goes.
 
I currently have a GTX 1070 FTW in my system powered by an EVGA SUPERNOVA G2 650W power supply. With the anticipated price drops coming with the release of the GTX 1080 ti I was thinking about picking up another 1070 FTW (new or used) and run them in SLI, however i'm not sure my PSU can handle it.
 
My research online seems to suggets that a 650W power supply should be able to handle a GTX 1070 SLI configuration, but I believe the FTW version of the card draws more power than other GTX 1070s. Even if I have enough wattage in my power supply I'm unsure if I can actually connect the power supply to the graphics cards properly. 
 
The SUPERNOVA G2 has 2 outputs labelled 'VGA' that each have a split into a 6+2 pin and a 6 pin. The 1070 FTW needs 2x8pin cables. So in order to avoid using adapters, i've used the 6+2 pins from two 'VGA' power cables, while the extra 6-pin is not used. However, theoretically I should be able to use a 6 to 8 pin adapter right? If I did that then I would have enough cables to fill up the 4x8 pin that is needed for a 1070 FTW SLI setup. If I also have to buy a new supply with 4 separate PCIe power outputs then the upgrade to a SLI configurations does not seem worth it.
 
I highly appriciate any help and I apologize for the large amount text.

Thanks a lot for your response, it's very helpful.
 
May I ask how you conclude how much watt I need and that 650W is too little? If you add the peak power consumption for the two cards, 2x215W, and add the 95W my i5 6600k needs you get 525W, which still leaves more than 100W for the rest of the system.
 
This guy over at LinucTechTips advices that 650W should be enough for 1070 SLI: outervision.com/b/yFpaY9
 
Also this power consumption calculator also seem to suggest that 650W is enough: linustechtips.com/main/topic/199255-how-many-watts-do-i-need-check-here/
 
Regarding the cables I thought I could get a 6 to 8 pin converter for each of the spare 6-pin connecters I have right now. I'm thinking that the cables draw from the same rail inside the PSU anyway so the only thing 2 less pins can limit is the amperage. But considering most other 1070s can function with a single 8-pin or a 8-pin + 6-pin i am not too worried.
 
EDIT: Had to strip http:// from the links in order for them not to be removed

500W is the minimum for 1 card in an AVERAGE computer.  That is calculating with the most powerful CPUs and usually 2 hard drives and 1 DVD drive.
 
I'll go through the individual numbers here:
The most powerful current CPU on the Intel side draws 140W.
Hard drives and DVD drives could theoritically draw up to 10W each.  Lets calculate with 2 HDDs and 1 DVD drive. 30W total.
There are no good numbers on power draw of motherboards, lets give it 75W, which is probably generous, but Im thinking a few USB ports that are drawing max power and plenty of other components.
 
So with these numbers, before you get to the GPU, you are at 245W.
You add on the single GPU at maximum power draw of 215W.
You are at 460W MAXIMUM.  Now the minimum power supply requirement is 500W which is low because it gives you no overhead with this setup.  Now these numbers are all under full loads.
 
Overhead is good for several reasons.  1 if you draw your PSU close to maximums for an extended period of time, you run the risk of burning out your PSU. 2 PSUs are most efficient at 50% draw and the drop when you start getting to higher power draws.
 
 
Source Wikipedia
 
To get the best performance and lifespan, you want to get to maximum draw of about 75% IMO.  So if your absolute minimums for 1 graphics card is 460W, then you are at 575W with a smart 25% total headroom.  If you go to 2 GPUs you are at 675W minimum, and with smart 25% total headroom, you are at 843W.  This gives you the efficiency headroom of 25% but no head room for expansion.  Hence my recommendation of an EVGA 850W Gold PSU at minimum and any of EVGAs 1000W as a good PSU with expansion headroom.