my build's power usage

[Apuu2011]

hello everyone i just upgraded to a sli of 2 gtx 1080's ti, but i think my power supply is not powerful enough cause does not run both the cards toghader.
Here is my build:
cpu: i7 6700k clocked to 4.4 ghz
ram: 16gb 2x sticks of 3200 mhz
gpu: 2x gtx 1080 ti
motherboard: asus gtx z170-a
cpu cooler: deepcool captain 240
fans : 4x 120mm , 1x 250mm
storage: 2x 500gb ssd, 1x 2tb hdd
leds strip, phanteks enthoo lux case leds. always at least one flash drive attached, keyboard razer blackwidow chroma v2.
power supply: corsair 750 watts.

so my question is is it actually power supply not powerful enough or something wrong with the gpu's ?

 

[profoundnoah]

Your PSU is more than likely the root cause here: What kind of monitor are you using to warrant SLI 1080 Ti's???? PCPP specs your build to be around 760W at max power draw, but that will more than likely increase with OC's. Is there something wrong that is making you think the GPU's are bad? For a new PSU, I'd look at 850W as the bare minimum and 1000W as a comfortable overhead.

 

[Greeko85]

Define "the cards don't run together". Is one of the cards not showing up/working when the system boots or are you unable to enable sli?

 

[superninja12]

MERGED QUESTION
Question from Apuu2011 : "system power usage"

Hello everyone, I just upgraded my build from a 1070 to 2 1080 ti, but one of the cards when in sli does not work (both of them works fine if not in sli), i thought at first a problem with the motherboard, but starting to think my power supply does not deliver enough juice to power the whole system. i will do a list of all the parts of my build, please help me understand if i should upgrade my power supply or change motherboard.
build:
power supply: corsair 750w
cpu: i7 6700k clocked to 4.4 ghz
ram: 2 sticks of corsair vengeance 16 gb each of 3200 mhz
gpu : 2x rog strix 1080 ti
motherboard: asus z170-a
cpu cooler: deepcool captain 240
storage: 2x 500 samsung ssd, 1x 2 tb WD hdd, 1x 256 gb hdd
fans: 1x 120mm, 3x 120mm with white LEDs, 1x 200mm
a strip of LEDs as well as case LEDs(phanteks enthoo luxe)
keyboard: razer blackwidow chroma v2
mouse: Logitech mx master
always at least 2 flash drive attached to the system.

have you got a sli bridge?

 

[rgd1101]

Please stick with 1 thread

 

[Apuu2011]

hello everyone, sorry if not answered back earlier and thanks for the help. So, first of all, to answer to superninja12 yes got an sli bridge, actually I bought a second one cause though the first one might be broken. To answer to Greeko85 when I run the pc in sli both of the cards boot up but after about 10 secs one of them (the bottom one) boots down. to answer to profoundnoah i'm using a Samsung 4k 60hz monitor(amd free sync).