When asked what the most important part of a PC build is, most people would say the graphics card or processor. While both are important, those answers overlook the component that keeps everything else running and healthy: the power supply. The power supply unit, or PSU, drives every part of your computer by converting the AC power from your wall socket to the DC power that your PC needs. With the right power supply, your PC will run quietly, efficiently, and smoothly. Get the wrong one, and it will refuse to boot, crash intermittently, or even damage the components.
Photo: Kevin Liu
Generally, the bigger and more powerful the PC, the beefier the PSU you’ll need. A small PC with a single drive and integrated graphics will only need 200-300 watts, while a more extensive system with multiple hard drives and a high-end graphics card may need upwards of 800 watts.
The simple answer? Use the Micro Center Custom PC Builder. Firstly, select the components for your planned PC, and the system will calculate the wattage you need and show you options.
Next, add in all of the components that you think you might add over the next few years, like additional hard drives, a better graphics card, optical drive and other bits. As you add each device, the system will update the wattage. This makes sure that the PSU you pick will keep your system running for years, otherwise you’ll have to rewire your entire system when you go to upgrade.
Watts, Wires, and Width: What The Numbers Mean
There are three critical factors in choosing a PSU: Watts, Wires, and Width. Watts considers how much power the PSU can deliver, while Wires is about how many (and what type of) connections it offers. Width is about making sure that the PSU can fit into your case.
Watts: How Much Power Do You Need?
The most important number with a PSU is wattage: how much energy it can output. The bigger the number, the more power-hungry components it can drive. You might assume that a bigger number of watts is always better, but a beefier PSU won’t make your PC run faster. A higher-powered PSU just allows you to power more components, like more hard drives. It will also provide more energy for adding new parts, like faster (and more demanding) graphics cards or additional hard drives.
The flip side of the wattage is efficiency. When you convert electricity from AC to DC current, you always lose a bit of power in the conversion. You’ll see this loss listed as a percentage. An 80% efficiency, for instance, means about 20% of the energy is lost in that conversion. More efficient PSUs lose less energy, which means lower electricity bills and less fan noise. That lost energy has to go somewhere, so it is released as hot air and driven out of the case by a fan. A more efficient PSU means less heat and less need for the fan to run. PSUs are labeled for efficiency, ranging from Bronze (about 80% efficient) up to Titanium (between 90% and 94% efficient).
Image: CLEAResult
Wires: How Many Connections Do You Need?
The cables are what connect the PSU to the components, such as the 20 or 24-pin ATX connector that supplies power to the motherboard, the 4-pin MOLEX or SATA connectors for hard drives, or the 6/6+2-pin graphics card connectors. A small PSU for a tiny system might come with just the ATX motherboard connector and a couple of SATA cables. In contrast, a large PSU for a big computer might offer several graphics card connectors and over ten SATA connectors.
That’s a lot of cables, so most larger PSUs go with a modular design where you only connect the ones you need. These modular PSUs come with multiple cables you plug in as you need them; leave any extra, unneeded cables in the box. This keeps the inside of the PC case tidy, but also allows for expansion. You can just plug in one SATA power cable for a single hard drive to start then plug in more SATA power cables when you add more drives.
That only works if there are enough connections, so think about how you might want to expand your PC over time. A small 200-watt PSU that can only power a couple of hard drives might work for a small system, but a workstation or gaming PC might need a larger PSU that has enough connections for lots of hard drives and a more powerful graphics card and enough wattage to power them.
Width: Choosing The Right Form Factor
Many years ago, PC manufacturers created Form Factors, or designs that set how big the inner parts of a PC should be. These cover things like how big the motherboard can be, where the screws go that secure the motherboard to the case, and what type of connections there are between the PSU and the motherboard. The different Form Factors have names like ATX, Extended ATX and Mini-ITX. For choosing a PSU, the critical part of the form factor is the size of the PS/2, TFX, SFX, and SFX-Narrow. All of this Three-Letter Abbreviation (TLA) salad boils down to one thing: if you have a specific case you want to use, check which Form Factor it is and which size of PSU fits it.
5 Great PSU Picks
The “I Can Power Everything” Option
Looking to build the ultimate computer? You’ll need the ultimate PSU to power it: the Corsair AX1600i. It’s the heavyweight champion of the PSU world, handling an incredible 1600 watts of power. It’s Titanium rated, so you get great efficiency to keep the power bills down when your PC is cranking. It is fully modular, so you only plug in the cables you need, and Corsair’s own iCue software provides a huge amount of data on how the PSU is performing and lets you customize everything.
The Above-Average Build
If you build pushes the definition of a mid-range PC, you might want to opt for a power supply with just a bit of extra oomph. Whether you're rocking an overpowered GPU or working hard with a high-end CPU, the Seasonic Vertex 1000 Watt Sakura Edition doesn't just look stunning, it'll keep your computer running smoothly.
The Sweet Spot Of Power & Performance
750 Watts is plenty of PSU for most PCs, providing enough to power the basics with some room for expansion. And you don’t need to spend much to get it: the Corsair RM750e will cost you less than a hundred bucks, but you get a fully modular PSU with room to expand. The gold rating means it is efficient and quiet.
Tiny But Tough
If you are building a small PC, you don’t need to compromise on the power of the PSU. The PowerSpec PS 750FXg is a fully modular SFX PSU that is only 5 inches deep but still includes a large and quiet 90mm fan and cables for up to eight SATA drives.
Cheap & Cheerful
Working on a bargain basem*nt build? The G-Skill 650-watt costs under $50, but still has a great range of features, including semi-modular cables (all of the Hard Drive cables are on one chain, not individual cables) and Bronze certification. It ain’t the biggest, most powerful or more efficient PSU out there, but it is great value for money.
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Richard Baguley is a seasoned technology journalist and editor passionate about unraveling the complexities of the digital world. With over three decades of experience, he has established himself as a leading authority on consumer electronics, emerging technologies, and the intersection of tech and society. Richard has contributed to numerous prestigious publications, including PCMag, TechRadar, Wired, and CNET.
