Varying errors and increasing numbers of errors suggest a PSU problem. Perhaps starting to falter and fail due to age, history of heavy use. Simply nearing its' designed in EOL (End of Life).
Or perhaps some defect bring the PSU to a premature end.
Two suggestions: 1) Some "house keeping" and 2) Swap in a known working PSU for test purposes.
Before doing either ensure that all important data is backed up at least 2 x to locations away from the PC in question,. Verify that the backups are recoverable and readable.
Suggestion 1:
Power down, unplug, open the case.
Clean out dust and debris.
Verify by sight and feel that all connections, cards, RAM, jumpers, and case connections are fully and firmly in place.
Use a bright flashlight to inspect for signs of damage: bare conductor showing, pinched/kinked wires, melting, corrosion, browned or blackened areas, moisture, cracks, loose or missing screws, scratches....
Suggestion 2:
Swap in another known working PSU - verify that the PSU has sufficient wattage to support the build but does not necessarily need to be 1200 W.
Be sure to use only the cables that come with the swapped in PSU.
The objective simply being to narrow down the list of potential culprits.
Continue watching Event Viewer and Reliability History for any changes: error codes and frequencies.
Warning and informational events are meaningful as well.