Just a quick thought. Since most arm dev boards servers are powered by USB, if we want to include power redundancy, it doesn't make sense to use a traditional UPS. Firstly, UPS storage capacity tend to be quite large compared to the meager amounts of power an ARM processor uses. Secondly, I'm no electrical expert but I believe storing the power at 5v reduces the amount of energy loss due to conversion of voltages repeatedly. Lastly, UPSes are more expensive compared to power banks which are run of the mill.
The only setback is that you require powerbanks which can output at up to 2A (which is required to charge tablets, or fast charge phones). However, since the server is connected 24/7, the input current has to be >= 2A, I have not found any such power bank so far, most seem to have a 500mA input limit. It seems people are willing to spend 8 hours to fully charge up their power banks to a level which is only sufficient to charge a fully dead tablet for 2 hours.