GTX 1080ti has a maximum power consumption (TDP) of 250 Watt. 6x250 = 1500 Watt. Better used 2x1000 Watt PSU, for keeping another part Of mining in good condition and for an along term mining process. for PSU can Corsair or EVGA.
250W is not a maximum of 1080Ti power consumption - it's typical TDP. The most overclocked models has 300W TDP. But with proper settings of 1080Ti your proposition is good enough. for 6x1080Ti 2kW PSU is neccessary safe minimum
I have never been anywhere near 250w on my 1080 Ti:s.
I am running five on a 1200w psu with some power to spare. (65% TDP)
I am sure i could run six cards if i tweaked it better. My psu can handle 1300w peak.
2kw is overkill imo if you dont have free electricity and live on the north pole.