Shut down, automatic startup when one PS to UPS and other to wall?

[Anonymous user]

We have a server with redundant power supplies but only one APC UPS .  The machine currently has one PS plugged into the UPS (A), and the other into a surge suppressor strip to the wall (B).  (It is a particularly vulnerable machine because it has a large RAID array but no battery backup on the controller.)  The two redundant PS are fed from two different circuits.  I don't see how to make this configuration handle all failure and reboot cases properly.  The BIOS is set to "always on".

Scenario 1.  All power fails.  Software learns from UPS that power is down, starts a shutdown which near or at the end orders the UPS to power off.  Either A or B powers back up first (or together) and the server will boot.  However, if A does not come up and B does the server will still boot but will then be unprotected and a subsequent power event on B would not be handled.  Will powerchute shut the machine down if it cannot talk to the UPS?

Scenario 2.  Power on A fails.  UPS signals machine to shut down, and it does.  However B still has power.  When power on A is restored does that count as a transition to "always on"?  The machine had power through B the entire time.

Scenario 3.  UPS on A fails.  If it does so gracefully (like over temperature detected, signal sent) the server shuts down.  If it fails catastrophically, or the USB cable falls out, does the software see this as a UPS failure?

It seems the goal should be to treat A as the sole power source, and have the server up or down depending its state, because it is unsafe to run the server on just B.   However, the only way I see to do that reliably is to plug both redundant power supplies into the UPS.  Or am I missing something?  I can poke around some more in the BIOS but in the first pass I did not notice anything like "ignore PS B for power state transitions".  The manual for the motherboard says only:

Restore on AC Power Loss
Use this feature to set the power state after a power outage. Select Power-Off for
the system power to remain off after a power loss. Select Power-On  for the system
power to be turned on after a power loss. Select Last State to allow the system to
resume its last state before a power loss. The options are Power-On, Power-Off
and Last State.

The motherboard is seen in Linux as "X8DTH-i/6/iF/6F/X8DTH, BIOS 2.1b".