Online UPS, Frequency : 50Hz

Online UPS is the best kind of UPS. Essentially, power from the wall outlet comes into the UPS, which has a battery in it. The PC system is then plugged into an outlet on the UPS which then supplies power for the system.
In this situation the PC does not draw power directly from the wall outlet. Instead it is constantly fed by the battery in the UPS. UPS continually recharges the battery, which is continually being drawn down by the PC system. This type of system provides the best protection and it's also the most expensive. Also, because this battery is continually being drained and then recharges, the batteries tend to go bad relatively fast.