Guys help me decide. Can I run 1080 FTW (-6286) SLI (no OC) on 850W PSU (EVGA P2)? It's brand new and I hate to buy another one.
 
On X99 5930K. It will be OCed to 4.4, + 5 SSDs+ 2 D5 pumps (new one from Alphacool VPP 755, which has half of power drain of ordinary D5) + 10 fans.
 
Power meter shows me 1000W, but if my math serves me well (for a humanist that's quite a statement LOL) - 215Wx2 + ~160W for CPU (running wattage meter on another 5930K 4.4 in the background with all cores loaded by BOINC compute 80%) and I get less than 160W. Plus 2 D5 with very pessimistic 50W and few SSDs (I plan to cut the number to 5 and put rest in external USB enclosure to limit clutter inside). What will be left is one 850 EVO 500 (system), one 950 Pro, one MX200 1TB, one 850 EVO 1TB and one 850 EVO 2TB. I consider changing MX and 1TB EVO to PCI-e AIC NVMe in the long run, just to cut more clunky cables. And finally 10 fans, probably NoiseBlocker 800-1000 rpm model, each is less than 1W - simply the only fan which never annoyed me, very quiet and just works). That will total at about 710W at most and I'm very pessimistic with SSDs, treating them as HDDs with each drawing 10W at least.
 
I'm tired of RAID cards and all that stuff. Want to simplify system. Existing workstation will be converted into one giant data pool and BOINC machine where I will throw all clunky HDDs I have.
 
Oh and EVGA thank you so much for US-only PSU coupon code. :P LOL

Try this PSU calculator
http://outervision.com/power-supply-calculator
 
 
my personal rule of thumb; expected Load  = 80% of PSU rating
 
Thought you CPU was rated at 140W, if your getting 160W - your working that really hard
 

Stability is important ---> more power
 
Happy to help

My GTX 1080 SLI rig uses 790 Watts maxed to date.
You are asking about the FTW Model Card I would add 100Watts.
Save Bet is a 1000 Watt Power Supply.

bcvnaugh is correct, I think 1000W is a safe bet

No. I'm really holding out for Ti step-up or will stick with single FTW if I get bored with waiting - project is long past it's time to start, but without final decision to go with 1080 or wait endlessly for Ti I can't really do anything. I said that end of March is probably (yeah probably, probably, maybe :P ) decision day as I want this rig up, running and working (not just put together) by 1st June. 
 
SLI for Andromeda is the only thing which hangs in the air. From reports I gather scaling is decent, but real performance gain is minimal - there is no such thing as sustained framerate of let's say 100 FPS in every moment, it can go down sometimes to below 50 which is daft (and I'm talking 1440p).  I would love to try it, but SLI is potential minefield. Problem is that I don't really need SLI. Never did. Andromeda is the only game I have which can benefit from this and shelling 1000 Euros (card, block, accessories, another PSU) just for one game... I strongly leaning into one card setup. Even my 970 does decent job when you disable AA-whatever (I really don't have head for all these meaningless acronyms who are complete mystery to my humble self). Performance jumped from 25 FPS to more reasonable 60.
 

I've just come across this post so it may be a bit late to  help out the original poster, but maybe others in the future will have the same question so I'll post anyway.
 
I have two GTX980Ti's in SLI on an X99 motherboard and PSU with power metering.  The 980Ti SLI power consumption will be a little bit higher than two 1080's in SLI when a game is GPU limited (the TDPs are 250W vs 180W, according to Wikipedia) but these numbers should give a good idea of the upper bounds of the PSU wattage required.
 
My system...
 
Motherboard: Asus X99-E WS USB3.1
CPU:  Intel i7-6900K (8 core, 16 thread, Broadwell-E), overclocked to 4.3GHz
RAM:  32GB (4 x 8GB) 3200MHz DDR4 @ 1.35V
GPU:  2 x GTX980Ti Superclocked, 2-way SLI + GTX1060 for Physx (all EVGA, of course!)
SSD:  OCZ/Toshiba 1TB M.2 card
Spinning storage:  1 x 1TB Western Digital black
Sound:  Asus Xonar Xense PCIe card
Optical drive:  Pioneer 5.25" BDR-207M Blu-Ray writer
Fans:  6 x 140mm
PSU:  Corsair AX1200i (1200W)
 
The Corsair AX1200i power supply can measure the actual watts consumed.  Here are the peak powers that I saw...
 
Desktop, with a web browser and a few background apps running:  170W
Prime95 + Furmark 4k stress test:  1100W
Prime95:  460W
Furmark 4k stress test:  720W
Witcher 3, 10 minute run around the starting village, 60Hz vsync set in Nvidia driver:  750W
Rise of the Tomb Raider, built-in benchmark, no fps limit (but got nowhere near 60fps):  700W
Batman, Arkham Knight, built-in benchmark, no fps limit (but no SLI):  550W
Borderlands 2, 10 minute run around Sanctuary & the Highlands, 60Hz vsync set in Nvidia driver:  610W
Bioshock Infinite, built-in benchmark, no fps limit:  650W
Bioshock Infinite, built-in benchmark, 60Hz vsync:  540W
Metro Last Light Redux, built-in benchmark, no fps limit:  740W
Half-Life 2 Lost Coast, built-in benchmark, no fps limit:  650W
Unigine "Heaven" benchmark:  670W
Unigine "Valley" benchmark:   660W
 
All were running at 4k (3840x2160) resolution with all graphics settings maxed out (except for silly things like chromatic aberation, motion blur, vignetting, film grain, etc. which I don't like but don't have much effect on GPU load).  I wasn't actually connected to a 4k display so the 4k output was reduced to 2k (1920x1080) using Nvidia's Dynamic Super Resolution in the driver.
 
For just playing games it looks like an 850W power supply ought to be sufficient for 2-way SLI, at least with today's games which don't seem to work many-cored CPUs anything like as hard as Prime95 does.  For running very high CPU loads simultaneously with high GPU loads at least a 1200W PSU is needed.  I would have liked to have fitted a 1500W PSU myself but my case is a bit too small to accomodate one without losing the ability to have an intake fan in the floor of the case.  With two GTX1080 cards instead of my GTX980Ti's you can probably shave at least 100W off these power consumption numbers, so an 850W PSU would be fine for gaming and a 1000W PSU would probably be adequate for anything else bar stress testing.  And if you don't overclock your CPU and stick to slower 1.2V RAM you could get away with reducing the size of the power supply a bit more.
 
On games where the GTX1080 easily hits 60fps and you use vsync or limit the frame rate you will get lower power consumption than me due to Pascal being more efficient than Maxwell.  On games where the GPU cannot hit 60fps or where there is nothing to limit the frame rate then the GPUs will just run flat out all the time (or as fast as the CPU can feed them) and power consumption will be fairly high (but still less than my 980Ti's).
 
Bear in mind that cheap power supplies often barely meet their output power spec when brand new in a cool environment with a cherry picked golden sample unit.  Most power supplies will also lose capacity as they age and when they get hot (dust-clogged intake vent on a summer's day).  Think about possible future needs too.  Will you be overclocking your CPU and RAM, going to a top of the range GPU with 250W TDP when Volta comes out, or stuffing your case full of hard disks?  My recommendation would be to buy a quality PSU from a reputable manufacturer and get one that has spare capacity so it's not running stressed all the time.  It should last you a decade, which is probably longer than any other component in your computer, so although it is undoubtedly expensive it's not so bad if you consider the cost being spread over many years.
 
Does anyone have actual worst-case power consumption numbers for an X99 2-way SLI GTX1080 system?   Or a GTX1080Ti one?

XrayMan
 
 https://www.evga.com/products/product.aspx?pn=120-G2-1300-XR      

And On Sale $190  A Great PSU. That is what my two GTX 1080Ti Cards are running under.

That 1000W G3 Gold PSU is surprisingly compact.  The 10 year warranty is reassuring, too.  I noticed that the fan stays off until 20% load and it looks pretty quiet when it does come on so the PSU shouldn't be noisy at all, although I would have thought the Platinum or Titanium PSUs with their higher efficiencies and slightly larger 140mm fans might be even quieter (but I didn't check that, and they're all larger anyway so they don't meet your space saving requirement).
 
My 1200W PSU's fan stays off until about 30% load, which effectively means it only comes on when I start gaming.  But once the GPUs get to work on a game their blowers are far louder than the PSU's fan so I never hear the power supply.  If, for some reason, I had to buy another PSU tomorrow I would definitely get another one which is silent at low loads.