Redundant power supply is to provide a second independent (alternative, parallel) power supply (insensitive to external conditions, including lightning and voltage decays) devices, which, due to their function must operate without interruption. They are connected mostly through RPS port (eg .: switch).
Such a support system of electricity supply in the event of a power failure includes a server rooms, government units, intensive care rooms and operating rooms. As a result, data devices can operate during a power outage. This can be compared to UPS functions (such as on-line), but much more efficient, because unlike them power outage may last considerably longer than just as much as sufficient batteries.