What does a power supply unit (PSU) do?

A power supply unit (PSU) is essential in electronics as it converts mains AC (alternating current) power into DC (direct current) power. Most electronic devices and components require DC to function properly, and the PSU ensures that the voltage levels are correctly altered and regulated to meet the specifications of the connected devices. This conversion is critical because many devices, including computers, require stable DC voltage for their operation, as fluctuations in that voltage can lead to malfunction or damage.

In addition to the conversion, PSUs also often include features to protect the connected devices from electrical anomalies, such as over-voltage, under-voltage, and surges. This protective role further emphasizes the importance of the PSU in maintaining operational integrity and reliability within electronic systems.

The other options describe functions that do not align with the primary purpose of a PSU. Modulating signal strength typically relates to frequency and amplitude changes in signals, which is a function of amplifiers or oscillators, not a PSU. Measuring the frequency of input current is a role suited for frequency meters or oscilloscopes, but not for a power supply unit. Enhancing audio quality pertains to audio processing equipment or sound systems, rather than the basic function of a PSU.