A computer buyer’s guide: The power supply

Hello and welcome to the final installment of our guide on how to pick the best components for your computer. No, don’t cry, this isn’t a farewell. This time we’re talking about picking the right power supply for your computer. If you plan on getting a laptop, you can skip this article entirely, for they come with the suitable power brick already in the package. But if you are shopping for a desktop system, or perhaps even building your own, read on, for the choice of the correct PSU can be quite daunting.

Wattage and efficiency

The wattage is how much power the PSU can provide and ranges from 300 W to, in the case of high end power supplies, 1500 W or more. But a office computer doesn’t generally need all that much power, and even a 300 or 430 W power supply unit will suffice. A higher wattage is important when you’re using very demanding components, like two (or even more!) graphics cards, RAID cards, high end processor, and so on. One way to gauge how much wattage your computer needs is to go to PCPartPicker, select the exact components you’re using and reading the figure on the top right corner. It’s not 100% accurate, but it gives you a rough estimate of the wattage you need.


Even more important than the wattage is the efficiency of your power supply, represented by a percentage. This number specifies how much of the power output of a PSU is actually usable by the components at 50% load: the rest is wasted as heat. Good power supplies conform to the 80+ standard, divided into 5 different tiers: bronze, silver, gold, platinum, and titanium. Each tier is more expensive than the previous. There is generally no good reason to get a power supply better than an 80+ Gold for a office build. Platinum and titanium power supplies are for servers running 24/7, where it’s vital to keep wasted power to a minimum.

Another interesting feature to look out for is smart fan, which detects how hot your power supply is running and decides if it’s the case to cool it down by activating the bottom-mounted fan. Despite the popular misconception, the fan mounted on power supplies doesn’t blow off waste heat, but sucks in air to cool the components inside. Heat exhaust is done at the rear of the unit, which is why power supplies have a grid there.


As with everything else about computers, a power supply will feature a number of connectors. Some of them come in fixed numbers and are essential to provide power to the motherboard and processors, whereas others may come in different numbers, depending on the model of your power supply and its wattage.

You should look out for SATA connectors, used to power your mass storage devices and optical drives, and Molex connectors, once used to power mass storage, but nowadays more regarded as “jack-of-all-trades” connectors. If you’re getting a PCI-E expansion card that requires a lot of power, like a RAID or graphics card, you should also pay attention to the number of PCI-E connectors your power supply comes with, and their type. Depending on the power requirements, your card may require one or two 8- or 6-pin connectors, or a combination of the two.

ATX power supplies

An ATX power supply
An ATX power supply.

If you’ve read the article about the motherboard, you probably remember the initialism ATX: It’s one of the motherboard sizes. In actuality, ATX is much more than that, because it also defines how a power supply is wired, how it connects to the motherboard, and so on and so forth. When IT people talk about an ATX power supply, they mean something rather specific, particularly a squared power supply with the size of 150 x 86 mm (d x h) and with a length that varies from 140 mm (the most common) up to 230 mm. The variance in length is due to the wattage the PSU provides and the advanced features it comes with, like modularity, which allows you to choose what connectors to plug into your power supply, making for a more elegant inside of your computer.

Chances are, if you’re shopping for a desktop computer, this is the power supply it comes with, unless you’re getting an extremely compact machine.

SFX power supplies

SFX is essentially an ATX power supply in a different form factor, sometimes used in some smaller micro ATX cases. It isn’t very common and you generally don’t need to worry about getting such a power supply.

TFX power supplies

A TFX power supply.
A TFX power supply.

These strange specimens are sometimes used in mini ITX cases or in pre-built systems with non-standard sizes. They are elongated and generally do not provide much power, which makes them a good choice for tiny form factors computers. You should be aware that the small fan will need to spin at a very high RPM in order to keep the unit cool, which means that inexpensive TFX power supplies can get quite noisy. It is very important, then to shop for a high-quality PSU, one that takes advantage of smart fan technology.

Pico PSUs

A pico PSU with its power brick.
A pico PSU with its power brick.

As the name implies, pico PSUs aren’t simply small: they’re tiny. They have no fan, take very little room, and are very efficient. However, they aren’t feasible for regular desktop computers, for they output very little power compared to ATX PSUs. They also cannot provide power to more than 2 internal storage devices, one through a SATA and one through a Molex connector. You cannot plug Pico PSUs directly to a wall outlet, but require a dedicated power brick, similar to laptop ones.

About Andrea Luciano Damico 137 Articles
Andrea Luciano Damico is a freelance translator from Italy. Among his interests are linguistics, technology, video games, and generally being a chill guy. He runs Let's Translate.it and Tech4Freelancers.net.