I use a small firewall that takes 5v 3amp power supply. It is called pfsense SG-1000. Sometimes the firewall OS can become corrupted in the event of a power outage. I want to make a small UPS that can go with the unit. I see there is already one for the raspberry pi but I want one to use with another device.

My budget is $60-$70 US.

Here is the firewall. https://netgate.com/products/sg-1000.html

about the same size as a rasberry PI