i've modded both Skyrim SE and Fallout 4 and this never happened to me. Modded meaning nearing MAX amount of plugins and mods. Check task manager and watch the RAM %, this was a big problem for me with 16 GB of RAM thanks to memory leaks in FO4. The worst that happened with me in the games are crashing to desktop. So it might be a bigger issue such as the PSU failing or what not.My rig:
MSI Z87-g55 Mobo
Intel i7 - 4770
16gb of Corsair ram
Zotac - Nvidia GeForce Gtx 780
Win7 Ultimate 64Bit
Evga Nex750G PSU
Is it really the PSU? Voltages look fine and temps look fine.