Computer power supplies are categorized by either internal desktop power supplies or external ones used for laptops.
Both types of power supplies convert the AC (alternating current), which a house is wired with, to the DC (direct current), the current the computer needs.
Internal desktop power supplies are rated by Watts. A computer with few drives and onboard graphics does not require a high wattage power supply. Whereas ones with high-end, or even multiple graphics cards, and or multiple storage devices require much higher wattage ones. Currently, power supplies can have as low as 250 watts and range to as high as 1000 watts or more. Having a power supply that has a higher watt rating than required is suggested to ensure all the devices have enough power. This is also a good idea to allow for future upgrades to the computer. Internal power supplies have multiple connectors that plug into the motherboard, graphics cards, and storage devices. Different sizes and shapes of these plugs prevent them from being plugged in incorrectly. These plugs and the devices they plug into are shaped so they will only fit with the correct alignment. This prevents damage to components from incorrect wiring. Before the modern type of connectors, the motherboard power was not modular and could be plugged in incorrectly. This could lead to damage and even destruction of the motherboard.
Internal power supplies normally have a fan to prevent overheating. In higher-end models, these fans have built-in temperature and load sensors. The power supply is “smart” enough to turn off the fan when the computer is performing light tasks and spin faster as power load and workloads increase.
Another feature that some power supplies have is modular wiring. In most power supplies, the wiring for the devices it powers is attached directly to it. This can lead to a tangle of unused wires inside the computer case. Modular power supplies have either some or all of these wires removable. This means that only needed wiring is used making cable management much easier. This is especially desirable for computers with see-through side panels that owners use for aesthetic reasons.
Laptop power supplies have lower wattage ratings, as laptops do not require as much. Laptop power supplies often have a removable power cord that plugs into the “brick” that transforms AC wall current to DC power the laptop can use. The other end of the power supply has either a small round column with an opening to plug into a receptacle with a hole and center pin on the laptop. Or more recently they use the USB C standard instead which has multiple uses besides just power.
The older style plug and pin type were often of different designs between laptops. Power supplies for laptops can be used to either recharge the battery while using it or not. As well they can be used to power the device in case of battery failure. To replace a laptop power supply at one time it had to have the same polarity, wattage, and column size as the one you were replacing. Modern USB C-style ones are less expensive as well as faster to charge the device than older style chargers. Most of these chargers are universal, to apply to all USB C devices, but be forewarned some are not, and it is best to consult the manufacturer. The USB C standard is becoming more prevalent and is also being used to charge and connect to smartphones and video game devices.
Power supplies are necessary for computer operation. If chosen correctly they can be operational for years without concern of failure.