A bit more digging on the diagnostics page of the RAID array reveals that the two power supplies actually failed on Jun 2 2017 at 10:21:00. Not surprisingly, this was the date and approximate time of the last major power glitch we experienced. Apart from this, the only other error listed on the diagnostics page is "Reading Error" on "IDE CHANNEL 2", but these errors precede the power supply failure.
Perhaps the power supplies are not really damaged, and its just in some funky state since the power glitch. After discussing with Jamie, I think it should be safe to power cycle the Jetstor RAID array once the FB machine has been powered down. Perhaps this will bring back one/both of the faulty power supplies. If not, we may have to get new ones.
The problem with FB may or may not be related to the state of the Jestor RAID array. It is unclear to me at what point during the boot process we are getting stuck at. It may be that because the RAID disk is in some funky state, the boot process is getting disrupted.
I am unable to get FB to reboot to a working state. A hard reboot throws it into a loop of "Media Test Failure. Check Cable".
Jetstor RAID array is complaining about some power issues, the LCD display on the front reads "H/W Monitor", with the lower line cycling through "Power#1 Failed", "Power#2 Failed", and "UPS error". Going to 192.168.113.119 on a martian machine browser and looking at the "Hardware information" confirms that System Power #1 and #2 are "Failed", and that the UPS status is "AC power loss". So far I've been unable to find anything on the elog about how to handle this problem, I'll keep looking.
In fact, looks like this sort of problem has happened in the past. It seems one power supply failed back then, but now somehow two are down (but there is a third which is why the unit functions at all). The linked elog thread strongly advises against any sort of power cycling.