Sometimes it is also just the power connectors not sitting entirely correct in their sockets. Had that once, PSU was totally fine but one of the PCI E power connecters got slightly loose (probably happened when I replaced one of the SSDs, simply by touching it). Bunch of strange CTDs and restarts until I checked all connecters sitting firmly in their sockets and everything was fine again.
Means: before you run for another PSU with more Watts, check the cables 