Which device provides power in an emergency when main power is lost?

• A. A generator
• B. A battery backup module
• C. An ordinary power supply
• D. Uninterruptible Power Supply

Answer: (D)

The key idea is immediate, seamless power during an outage. An Uninterruptible Power Supply (UPS) is designed to take over the moment input power fails, using its internal batteries and switching electronics to keep the connected equipment running without a pause. It also helps by conditioning the power to protect sensitive devices.

A generator, while useful for longer-term backup, isn’t instant. It needs to start up and transfer control to it, which creates a brief interruption unless a pre-start and automatic transfer system is in place. A battery backup module stores energy, but without the instant switching logic of a UPS, there isn’t guaranteed seamless power in the exact moment power is lost. An ordinary power supply cannot provide energy when mains power is gone; it only converts AC or DC under normal supply.

So, the device that ensures power remains available the moment main power disappears is the Uninterruptible Power Supply.