Online UPS is a UPS (uninterrupted power supply) where the ups is directly connected with backup line even when electricity is present and when power goes off, it does not have to switch to the backup so there is very little or no delay to switch over backup power supply. Offline UPS however is different. It charges the battery when the electricity is present and then switches over to the backup power when the electricity goes off. This UPS (offline) may cause a little delay like 200 ms to give backup.
