Uninterrupted power system and controlling method of the same

The present invention discloses an uninterrupted power system (UPS) and a controlling method for the same, which comprises a current-leakage prevention unit, an independent power-supplying circuit, a signal circuit, and a database for storing pairs of data of power consumption corresponding to estimated-remaining backup time, so as to achieve below technical effects that: 1. More exactly shut-down time provided for user's judgment; 2. Prevention of abnormal power; 3. Optimal usage of the backup power; 4. No occupying a space where the interface card is positioned and avoiding a malfunction of involving the electronic device connecting therewith; and 5. Inspecting the super capacitor and the exterior power all the time.