Only 4 years later.
But with experience to add. And given that I came to this after the fact, rather than doing my research beforehand, anyone wiser than me could do with the up-to-date experience, so they know nothing has changed.
I purchased two KDM Power brand PSUs from eBay (once again: trying to jump on the "cheap" bandwagon).
Both builds start with this base:
MSI Z370-A Pro Mobo
Intel i7-8700
16GB RAM (G Skill)
EVO 970 500GB M.2
3TB HDD
KDM Power 875W PSU
Build #1 uses a GTX 1070Ti, air cooled, no problems.
Build #2 uses a GTX 1080Ti with hybrid cooler, and after 1 hour of continuous gaming, the PSU blew up. EVGA says this GPU should only need a 650W PSU, and I had an 875W PSU...
Thank God when I plugged in the other PSU, everything kept working, but I'm definitely forking over the money for an EVGA G3 type PSU, probably 1000W, just because I'm suddenly very gun-shy about not having a big enough PSU, and an 875W was already "not big enough".