Did you clock down the CPU? Clock down the RAM? Reseat and clean the RAM stick? Reseat and clean the GPU? I mean, your homework before to RMA?
Random reboot is not always the PSU.
https://www.techsupportforum.com/forums/f25/solved-random-reboots-on-my-pc-805305-9.html
https://forums.tomshardware.com/threads/computer-keeps-restarting-on-its-own-already-changed-psu.3064200/