Offline UPS works the simplest among different types of UPS. Its functions are mainly surge protection and battery backup. When the mains power is stable, offline UPS runs bypass mode and the device is directly connected to the mains power. In case there is a sudden blackout, offline UPS will mechanically switch from the mains power to DC-AC inverter output (from battery) in less than 25 milliseconds in order to avoid equipment shutdown. The backup time varies depending on the capacity of the battery as well as degree of loading.

KEBO online UPS is safeguard for environment where electrical isolation is necessary and also for equipment which is sensitive to power loss. The initial cost of online UPS is generally higher than line interactive UPS, but the total cost of ownership is lower due to longer battery life. The online UPS is a necessity when utility power sags, outages and other anomalies are frequent. This is very critical when protection of sensitive IT equipment loads is required.

The basic principle of online UPS is the same as an online or line interactive UPS. However, it has a much higher price due to much greater current AC-to-DC battery-charger rectifier, and with the rectifier and inverter designed to run continuously with improved cooling systems. It is called a double-conversion UPS due to the rectifier directly driving the inverter, even when powered from normal AC current.