Gotcha. Here is one for AC that is smaller than most:
SKE Compact Size 425VA/240W UPS Battery Backup & Surge Protector for Computer UPS Uninterruptible Power Supply UPS Phoenix VL425
11.7″D x 3″W x 6.7″H
I’m not sure why you need separate power supply connections for the controller cpu or a battery charge controller.
Just plug in the 24v transformer into the UPS and it should keep OpenSprinkler on as well as provide power to open the valves when needed. It should help with short power outages. If you want protection from long power outages, you’ll need a much larger UPS.