Thanks for attempting the update, and I'm sorry it didn't fix the issue for you. I'm trying to see where Synology mentions what upstream version of NUT/upsd they're using, although I'm struggling to find it so I think we can only assume that they're still using an older version here. Can you troubleshoot the docker container further to at least get to the point where you can confirm that it presents the data correctly?

I'm sorry to say that this is starting to reach my limits of knowledge as well as I don't have much experience either with containers in Synology or running upsd in a container. Is there any chance you have another machine to test that can run upsd in a more traditional physical OS or even a VM, just to confirm that the issue would be fixed?

No.... Synology's DSM is almost, but not quite Linux, so I used to have a very old X58 PC with a 1st gen Core i7 where I ran Ubuntu for playing with things like this. Something died and even the cheap engineer in me said it wasn't worth the time to try to fix. This UPS issue is the first thing I've run up against since I scraped that old PC where I want a Linux box to play on.

So, my options seem to be:

1. Poke at Synology (just submitted a service request)
2. Try to ask the container author for insight as to why it won't run
3. Build a Linux sandbox machine and try to build my own container (not just for this.....)
4. Deal with a funky "Output Voltage" display (most likely)

If anyone is interested, I just heard back from Synology.
"I have received an update from our developers, and the NAS is using Network UPS Tools (NUT) with Driver 2.6."
https://archive.synology.com/download/ToolChain/Synology%20NAS%20GPL%20Source/7.2-64570
I downloaded the file for my DS416Play (INTEL Celeron N3060 - Braswell) and poked around - the last entry in the change log is dated 5/31/2012. My response back to Synology equates to "please update with the latest version".

Can we all say OMG!!!

Thank you for looking into this and posting back with results! I wonder what the chances are of Synology coming through with an update. Do you think you'll look further into the container idea?

1. I have no idea how responsive Synology will be. In my opinion it's not a good business practice for them to ignore something this old if they don't want users bashing DSM now that the details of this extremely obsolete driver have been discovered. Makes me wonder how many other drivers are out of date and being ignored by Synology.
2. I sent an email to an address I found buried the container's image history. I'm waiting to see if anyone responds, but at least I haven't gotten a "no such address" bounce back.