Decent 750W should be OK, but if old PSU could be it has degraded.
I'm on 850W, HW as in my sig, with 9x 120mm fan, 2x 140mm fan, D5 pump, RGB on WB and case.
Max draw from wall my system been ~650W AC side, CPU/RAM/GPU OC'd.
Decent PSU are rated DC side, so the 650W from wall ~585W if 90%...