

I just read the manual for the Euro version; basically, they assume you take the power strip/PDU with the computer.
So, you plug the special UPS into a spare outlet on the PDU; it monitors the power supply, and as soon as power from the PDU drops it jumps in and starts supplying. So plug into an outlet, then unplug the PDU from power, and the UPS takes over. Since at this point the pins on the PDU plug are live, they provide a safety cap to put over the end of the cable. The computer itself is never unplugged.
Just throwing this in here as another thing to consider - instruction set. From a quick check (so I’m happy to be told I’m wrong) the Celeron & Pentium options don’t support AVX. That means some stuff - and I’m giving a hard stare at MongoDB here, but there will be others - is not going to run, or at best you’re going to be either stuck with old versions or recompiling yourself from source.
(I don’t know if any of your apps require Mongo or AVX, but I was bitten by this in the past and it was one of the main reasons I eventually upgraded one of my small clusters.)