It's a strange one, but it does seem like an issue with the PSU. Can you just confirm these...
1) That there's no uninterruptible power supply equipment connected to the system
2) That this happens both when trying to resume from sleep and from a system shutdown
Failing that, you really want to debug with a different PSU. Maybe take the system to somewhere local, or a loan one from a friend.
13900KS / 8000 CAS36 / ROG APEX Z790 / ROG TUF RTX 4090