A UPS is not limited by equipment type and ensures uninterruptible power to computers, data centers or other electrically powered equipment during an unexpected power failure.

UPS units vary depending on the protected equipment size, which can range from a single computer to entire data centers, buildings or cities. When sensing normal power fluctuations or interruptions, a UPS may automatically activate backup systems to ensure that data is not lost. Many technologies are employed to increase the effectiveness of modern UPS systems, including the following:

• Offline/Standby: Restores power when normal power fails by using a DC/AC inverter output that is usually no longer than 25 milliseconds.
• Line-Interactive: Ensures power for five to 30 minutes and up to several hours with expansion, by using a multi-tap, variable-voltage autotransformer, which immediately adds or subtracts the a transformer’s output voltage.
• Double-Conversion Online: This is similar to line-interactive, except that a rectifier directly drives a DC/AC inverter, even when it is powered by a normal AC current. This is typically a high-cost option.

UPSs may monitor their status (battery charge and readiness to perform) and report deficiencies or issues to the protected computer via a serial port, Ethernet or USB connection.