What is a PSU?

• A. Power Supply Unit that converts AC (or DC) to server DC rails with protections.
• B. A software module that manages power planning.
• C. A peripheral that provides network connectivity.
• D. A fuse block used in data centers.

Answer: (A)

The main thing being tested is that a PSU is the Power Supply Unit, the hardware component that takes input power from the facility (AC, or from a DC supply) and converts it into the DC rails that the server components need, while also providing protections such as overvoltage, overcurrent, and short-circuit protection. It also regulates and delivers the correct voltages to parts like CPUs, memory, and drives, and in many servers it can be hot-swappable and provide redundancy for higher availability. Other choices describe software for power planning, a network device, or a fuse/distribution block, none of which are the component that actually powers the server with regulated DC rails.