as title says.
Depends on your cpu, I would add ~200w to you build site estimate and call it good.
850 watts depending on your build.
Also--SLI support is almost non-existent with the 1080ti and has severe diminishing returns. In some games, it even sees decreased FPS, and with games that do support SLI, you're only looking at a gain of 5-10 FPS. So really, you're paying for looks. Just something to be aware of.
Thank you for the information! Right now my build is i7-7700k, Asus maximus IX hero, 16gb ram 3200mhz, Strix 1080 ti, 750w g3 PSU.
750W will be plenty for you then.
Unless you have some crazy build 750W should be good.
I'd probably just go for the full 1000W so you can brag you've got SLI and a massive PSU =P