Which of the following is NOT one of the main form factors for power supplies?

The correct answer is Micro ATX, as it does not refer to a power supply form factor; rather, it is a motherboard form factor. Micro ATX motherboards are designed to fit within certain physical dimensions to allow for compact system builds, but they do not define the specifications or design of power supplies.

In contrast, AT Extended (ATX), ATX12V, and AT are all recognized form factors for power supplies. ATX power supplies provide the necessary connections and deliver the appropriate power for components adhering to the Advanced Technology Extended specifications, which became standard in modern desktop computers. ATX12V is a variation that supports additional power requirements for high-performance systems, and the original AT form factor was used before the widespread adoption of ATX standards. Understanding these distinctions is essential in system building and compatibility considerations.