What Does A Power Supply Do?
A power supply’s job is to convert an Alternating Current (AC) signal coming from your wall outlet into a usable Direct Current (DC) signal. Simply stated, this process is done by stepping down the input voltage level with a transformer and then rectifying it to convert to DC. Once the DC signal is generated it is used to power all the devices and components of your system. In order to distribute the signal around to every component, many internal or external splitters can be attached to satisfy the number of connected devices. Usually a preset number of leads are provided by manufacturers to make this splitting procedure simple or even unneeded to the end user (as proper voltage values must adhere to specifications). From there, voltage regulation (often in the way of capacitors) is used to prevent your power supply from outputting too much or too little power. This protective mechanism is often called over current protection, over voltage protection, or over power protection. It is always important to ensure that your power supply has built-in regulation capabilities or spikes / sags due to fluctuations from the supply could damage your components. Alternatively, connecting your power supply to an Uninterruptible Power Supply (UPS) unit can greatly eliminate any potential harm due to external conditions on the unit.
For computers the power supply is most responsible for providing power to the motherboard, your hard drive, CD drives, expansion cards, etc. In most cases, a single PSU unit (as opposed to a redundant power supply setup where multiple PSUs are cascaded in case one fails) is responsible for powering all parts internal to the system. Some external devices such as keyboards, mice, and external drives may also draw power either directly or indirectly from the power supply. This makes the power supply a critical component to the system. That’s why when the power supply fails, your system will no longer operate.