In a redundant PSU setup, what is the purpose of having a spare unit?

• A. To allow for higher peak power usage.
• B. To reduce energy consumption.
• C. To maintain uptime during a failure by providing spare capacity.
• D. To improve cooling efficiency.

Answer: (C)

Redundancy in power supplies is all about keeping the system online even if a power supply fails. Having a spare unit means there’s a ready replacement that can immediately take over the load, so the system continues to run without interruption. In practice, PSUs are arranged in configurations like N+1 or 1+1, where the healthy units share the power load and a spare can automatically assume full responsibility if one unit goes down. This is what preserves uptime and prevents a single PSU failure from bringing down the entire system. It’s not primarily about allowing higher peak power, reducing energy use, or improving cooling; it’s about reliability and continuous operation.