If your temps are within the reason, it's safe to assume it's the PSU who is acting up.
While Seasonic SS-750KM is good quality, it's also past it's lifetime. SS-750KM came with 5 years of warranty and the PSU platform itself is 10 years old (first launched in 2009). You getting more out of it than it's warranty length was, is common with Seasonic PSUs but nothing lasts for forever. Here, i'd retire the old workhorse and go with new, up-to-the-date PSU.
Without knowing your full system specs, i can't say if 750W PSU is needed at all or if you can go with a bit cheaper, 600W range unit. For 700W range unit, i suggest getting any of the following Seasonic units: Focus 750 (80+ Gold), Focus+ 750 (80+ Gold), PRIME Ultra 750 (80+ Platinum) or PRIME Ultra 750 (80+ Titanium),
pcpp:
https://pcpartpicker.com/products/compare/64cMnQ,gWbwrH,hKc48d,cNsmP6/
Warranty wise:
Focus: 7 years
Focus+: 10 years
PRIME: 12 years (includes all PRIME models: regular, Fanless, AirTouch, SnowSilent, Ultra)
All 3 of my PCs: Skylake, Haswell and AMD are also powered by Seasonic. Full specs with pics in my sig.
Also, PRIME Ultra 750 (80+ Titanium) is the best 750W PSU money can buy at current date and with it, you'll get the highest efficiency (93%), tightest voltage regulation (0.19%), longest hold-up time (30ms), lowest ripple noise (16mV) and longest warranty (12 years) there is. Fully modular cables and toggle-able Premium Hybrid fan control too.
specs:
https://seasonic.com/prime-ultra-titanium
review:
http://www.jonnyguru.com/blog/2018/07/03/seasonic-prime-ultra-750-titanium-power-supply/