An uninterruptible power supply (UPS) is a battery-backed unit placed between the wall socket and sensitive equipment. When mains power drops, it switches to battery instantly, giving time to keep running briefly or shut down safely. Most also smooth out spikes and dips.
Capacity is rated in volt-amperes (VA) or watts and runtime depends on the load. A small unit may keep a router, switch and a till going for 15 to 30 minutes, while larger ones support servers. Some units report their status over the network so an alert is sent when mains power fails.
Stores and venues commonly protect the comms cabinet (router, switch, NBN box), the back-office PC or server and sometimes the main till. Keeping the network up means card terminals and cloud POS can carry on during a brief outage, particularly where terminals use mobile data.
A UPS does not run a whole store through a long blackout, and batteries wear out, typically needing replacement every few years. Check the size against the actual load, test it occasionally, and do not plug heat-producing items like fridges or coffee machines into it.
It is a modest cost that prevents corrupted data, damaged hardware and lost sales from brief power glitches.