I purchased a second hand Supernova P2 and it appears to work okay when the PC is on, although maybe it doesn't seem to put out 1200W (long story). That said, when the PC is turned off (running linux "# shutdown -h now"), the PSU fan goes to high and stays there as soon as the PC power turns off. It's used on an old Supermicro X8DTH-IF dual xeon board. There are a couple of case fans plugged into the molex connectors that turn off with the PC, but the PSU fan goes into screamapillar mode as soon as the rest of the computer fans stop. I feel like there's something wrong with it. AFAIK, the 10 year warranty only applies to the OG purchaser, so I think that I'm SOL on the warranty.
 
Same behavior regardless of the "ECO" mode switch setting.
 
Suggestions on how to fix it? I've worked on a lot of electronics and no problem opening it up to make a correction if there's a known issue. Anyone who's seen this before and knows what's going on would save me trying to troubleshoot the thing. Thanks.

Hi ala.frosty,
 
That is odd behavior as the GPU fans should obviously stop as well as the PSU fans.  I am assuming that the operating system is shutting down, but that the motherboard is not turning off the power supply or instead rebooting and locking up, as the GPU fan is going full blast as well. 
 
I suggest to double check if there might be a BIOS update for the motherboard, to see if this helps, and looking into the Linux build for help as well.
 
 

try "poweroff" command (-P) as your not using any delay timer anyways with the "now command"

 -P

poweroff


systemctl poweroff
 
 
Test the PSU isolated from the PC, with the "24-pin test cap" or the jumper method (see FAQ)
 
FAQ:  How do I test my power supply?

ala.frosty
So, I replaced the PSU with a Corsair unit and it turns out what I thought was the PSU fan going mental was actually the MoBo CPU fans going to high and the mobo performs the same with the Corsair unit exactly as it does with the EVGA unit. 
Which is to say that as far as I can tell, this is nothing to do with the EVGA PSU.

Sounds like a Linux issue but then again check the motherboard BIOs to see if there is a setting for each individual fan header that can be adjusted.