While the 790 SFF's tiny 240W PSU with its 17amp +12V rail isn't technically enough for the Zotac GTX 1050 Ti low profile gfx card...
I'm using the Zotac GTX 1050 Ti in my Optiplex 790 SFF.
http://imgur.com/a/Ro2ln
So far, so good with games that max out both the CPU and GPU at 100% usage. But I suspect something will eventually give out. And there are no PSU upgrades for that PC either.
Yes, there are probably better cheap and/or refurbished PCs to buy for gaming. Find a PC that is a mini tower that takes a full height card and has a 300W or better PSU if you don't want to chance the Optiplex SFF.