Standby power, also known as backup power, is a type of power that can be a source available to the data center that takes over the function of supplying when utility power is unavailable. Standby power systems are designed to provide power to critical loads in the event of a power outage, and can include generators, uninterruptible power supplies (UPS), and batteries. Standby power systems can be used to provide power to the data center for a short period of time, such as a few hours or days, until utility power is restored.

Passive, Active and Alternate are not specific type of power sources used in data center. They are terms used in different context and have different meaning.