Does anyone in this community have any experience managing Network UPS?

I purchased an "APC 3000VA Smart-UPS" (https://www.amazon.com/gp/product/B0785NCFMY) in 2020. It's been performing exactly as it should ever since, and life is great.

However, when I've had it, I have experienced two or three "catastrophic" power outages (line utility goes out), and the UPS kicks in and does exactly what it is supposed to do.

My problem is that in the time between buying the UPS and now, my homelab has grown significantly, and in one of those power outages, I overestimated my battery time, and my entire stack died while I was fucking around with one of the servers.

In my most recent power loss, learning from the past, I raced downstairs at 2AM with all the UPS alarms beeping loudly, and I raced to shut down the stack properly, knowing (this time) that I'd only got about 5 minutes of life. I got everything shut down this time, which is good—but it forced me to take a good hard look at some kind of Automated Shutdown.

I've known for a long time that these things could happen, but I've never had a need to investigate. Well, here we are, LOL.

I have the APS UPS connected to my switch, and it is getting a DHCP IP -- and I can see ARP requests going back and forth -- my pfSense FW shows that it is sending/receiving data -- albeit just a few kilobytes here and there, but I know there is TCP/IP life on it -- but I'm at a loss beyond that.  I've tried to SSH to it, but I just always get a "Connection Refused" -- using the "default" credentials I found online, "apc/apc"... 

So yeah, anyone out there with any background or experience with Network UPSs, I'd love to chat with you to figure out how I can get into this thing and make it do what I'm absolutely certain it's capable of doing!

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Thanks,
Alex.