Hi there,
I took the liberty of looking up the units you’re currently using and I noticed they’re PWM sine wave. I wonder if this might be the culprit.
Typically products like POE switches need to have a pure sine wave power fed to them in order to stay up and running during power outages.
To provide a brief example of the two, think bumpy road (PWM sine wave) vs. smooth road (pure sine wave). The longer you drive your car on a bumpy road the more wear and tear on the car. Also some vehicles can’t travel down bumpy roads–same thing with POE and PWM sine wave.
So I would suggest leading with the UPS system that has a pure sine wave and possibly even a unit that has true online double conversion technology.
With a true online unit, the UPS system is always running off and charging the battery so any power issues are immediately caught and provide nothing but a seamless power.
Firewalls are typically about 30 watts and 48 port POE switches are maybe at most 750 watts (780 watts total). For this I would suggest leading with the SU1500RTXLCD2U:
http://www.tripplite.com/smartonline-120v-1.5kva-1.35kw-double-conversion-ups-2u-rack-tower-extended-run-snmpwebcard-option-lcd-display-usb-db9-serial~SU1500RTXLCD2U/
This true online UPS system will support up to 1500 va/1350 watts, has a 15 amp plug, and six 15 amp outlets.
At 780 watts the unit alone will provide about 11 minutes run time, which is really all you need to shut the equipment down, but if longer runtime is needed add the BP48V24-2U:
http://www.tripplite.com/external-48v-2u-rack-tower-battery-pack-enclosure-dc-cabling-select-ups-systems-bp48v24-2u~BP48V242U/
This will bring the runtime to about 52 minutes.
To recap, the following has been suggested:
qty. 1 SU1500RTXLCD2U
Qty. 1 BP48V24-2U
If you have questions please feel free to ask them in the thread or even send me a PM.