TNAS with UPS starts safe mode on AC powered ON

[realdvk]

I have strange behavior with UPS APC BE700-RS connected via USB. Today I decided to do some tests on UPS. UPS is configured to enter safe mode 1 min after power loss. Test was simple: I just unplugged UPS from the AC power for 20 seconds. My UPS is rated for 405W and my setup consumes about 300W of power. So, then AC power is OFF, my UPS immediately enters LOW BATTERY mode (beacause of high enegry consumption). Safe mode was triggered successfully by TNAS.
The strange behavios is that TNAS does not recovers from safe mode on UPS AC power restore and continues to be in safe mode for long time. Reboot does not help. Web UI is not worked. I disconnected the UPS USB cable and rebooted the TNAS. Web UI is now working.
The next strange behavior is that when I plug the UPS back in (AC powered), the TNAS immediately goes into safe mode (confirmed by /etc/upslog/2024-01-07.log).
Why the safe mode is triggered regardless AC power is ON on the UPS?

[mmalchuk]

This is because your UPS not supported by NUT (Network UPS Tools).
Check HCL here: https://networkupstools.org/stable-hcl.html