The power supply is the most neglected component on the computer. Most users will spend a great deal of time choosing a new processor, video card, and motherboard, but when it comes to the power supply must users try to be cheap. Don’t be. By not caring about your power supply, you will be paying a higher electricity bill and will be putting your equipment at risk.

Efficiency is the parameter that measures how much a power supply consumes for its own operation, and it is expressed by the mean of a percentage. This percentage tells the difference between the wattage the power supply is delivering on its outputs and the wattage it is pulling from the power grid. For example, if a given power supply has 80% efficiency, this means that when delivering 200W on its outputs this power supply is actually pulling 250W from the power grid (80% of 250 W is 200W). This 50W difference between the two is the amount of power the power supply consumes to operate and it is completely wasted – but you pay for it.

A power supply with higher efficiency will consume less power from the power grid to produce the same wattage on its outputs. If we replaced the power supply above for a unit with 90% efficiency, we would now pull 222W from the power grid, saving 28W compared to an 80%-efficiency unit. This way a power supply with higher efficiency will reduce your electricity bill. This way you should pick a power supply with the highest efficiency your pocketbook can handle.

We want basically five things in a power supply:

• First, that it is an honest product and can deliver the wattage its label says it is capable of. Unfortunately, the average user can’t tell this by just reading the box. But in United States, it’s becoming less and less common to find power supplies that can’t deliver what is written on the box.
• Second, the highest efficiency possible, as already explained.
• The third thing we want is that all outputs from the power supply stay inside their allowed values all the times. If you have a power supply that is for instance delivering +13 V instead of +12 V this will overload your components and may lead to computer crashes and even burning components.
• We also want the outputs from the power supply to be as “clean” as possible, without electrical noise or fluctuations (“ripple”).
• And finally we want the power supply to have protections, so it will shut itself down if something wrong happens, reducing the risk of having your components burn.

(Gabriel Torres is the editor-in-chief of Hardware Secrets, a leading technical website with the goal of uncomplicating the complicated when it comes to PC hardware.)