Other contributors have said "Off line ups and online ups?" is the same question as "Offline ups and online ups?" If you believe that these are not asking the same thing and should be answered differently, click here
Simple Explanation:
Online UPS is an uninterruptible power supply that has no cut-off or sudden interruption during the switch-over transition of the power used to bypass or to battery source while...
An off-line UPS remains idle until a power failure occurs, and then switches from utility power to its own power source, almost instantaneously. An on-line UPS continuously powers the protected load...
In an on-line UPS the load is always being powered by the UPS and it is constantly charging so there is no switchover time. In an off line system, the system detects the lack of voltage and switches...
A UPS is an 'un-interruptable power supply' - they provide back-up power in case of mains failure, to enable a file-server to maintain its functions. They work by having a re-chargeable battery...