What should I check after my PC abruptly shut down during a possible power flicker?

You can run CHKDSK to check the file system, but it may need to be launched from an elevated Command Prompt and can require a restart if the system drive is in use. For example, `chkdsk C: /scan` performs an online scan, while `/f` schedules repairs. There is generally no need to use `/r` on a healthy SSD unless you are investigating suspected drive problems.

The UPS behavior is worth investigating separately. A standby or line-interactive unit can take a few milliseconds to transfer to battery, while an online double-conversion UPS continuously supplies power through its inverter and does not need a transfer. Check the UPS event log, battery condition, load, and whether it is configured to react to very short dropouts. The replacement unit may work better, but it is still worth testing it with a safe, controlled unplug test.

If the computer starts normally and everything is working, it is probably fine. Modern power supplies include protection circuitry, and a single unexpected shutdown does not usually cause lasting hardware damage. You can check Windows Event Viewer for the unexpected-shutdown entry and run a system-file check if you want extra reassurance. Also make sure your important documents are backed up.

A brief power interruption is different from a damaging surge, and the fact that other appliances stayed on suggests this may have been a very localized or momentary interruption. If the PC continues booting normally, does not show disk errors, and has no new crashes or hardware symptoms, there is not much else to repair. Keep backups and monitor it rather than repeatedly running intensive tests.