What type of current does an uninterrupted power supply use?

Uninterrupted power supply (UPS) is a stand by battery. Charged with mains power, it is designed to give out DC current should the mains power suddenly goes off, long enough for computers to be shut down properly, so avoiding corruption of data and the computer system. I believe that in some larger commercial/military/Government organisations, an inverter DC to AC is in their larger capacity UPS systems, to continue on AC until the mains power is restored.

Another Answer

A UPS is often used to supply computers, in order to protect their data in the event of a power failure. They consist, essentially, of a battery charger, a rechargeable battery, and an inverter. The main power supply maintains the charge on a battery, via a battery charger, and the battery's output is converted to an a.c. output via an inverter. Voltage values are maintained by internal Transformers.