The Power Supply Unit (PSU) might not be the most frequently discussed PC component, but it’s a critical piece of any desktop. Supplying power to your entire system is an extremely important role, and using the wrong one could be costly.
That’s why we’re going to cover the basics of power supplies, and provide you with the information you need to understand why having the right PSU is important, and why simply settling for the cheapest option is not the best solution.
Let’s kick things off by going over the different cables power supplies use to provide power to your system.
Though the PSU you purchase should come with all of the cables you need, it’s worth knowing what the individual connections look like. The exact cables you’ll use will vary depending on the specifics of your build, but you’ll most likely be dealing with the following:
- 24-pin Motherboard: The way power is allocated varies from motherboard to motherboard, but the 24-pin connector/cable is frequently used to power important features such as the chipset and PCIe*
- 4/8-pin CPU: This connector provides power to your CPU. Modern CPUs draw more power than the 24-pin motherboard configuration can provide, which is why the additional 4/8 pin cable came into use. Though it can vary depending on the manufacturer, the CPU cable usually plugs into the top left side of the motherboard, near the I/O on a standard layout
- 6/8 pin (PCIe*/GPU): Some GPUs draw enough power from the PCIe* slot, while others require a specific power cable configuration to operate properly. Most PSUs address this required flexibility by providing cables that can be used in a variety of combinations, some of which include 6, 8, 6+6, 8+6, and 8+8, and even 8+8+8 pin connectors. PSUs will often provide multiple connections on a single cable to avoid having to run additional wires, and for the vast majority of users, this will function the same as running multiple cables. Be sure to double-check that your power supply has the connections you need for your GPU before purchasing
- SATA Power: This connector is used to provide power to SATA storage devices. Other devices have since adopted the standard as well, such as RGB hubs and fan controllers. Many PSUs have multiple SATA connections on one cable to reduce the amount of cables required
- 4-pin Molex: This is an increasingly rare legacy connector that has mostly been replaced by SATA. Molex connectors are usually found on less common accessories, such as water cooling pumps
How Many Watts?
When selecting a new PSU, one of the most common questions asked is, “How many watts is enough?” As is often the case in the world of PC hardware, the answer varies widely depending on the unique needs of your system.
Generally, more complex systems require more power to run. A desktop with a custom liquid cooling loop, a high-end motherboard, and dual GPUs is going to need a higher wattage computer power supply than a simpler system.
It’s impossible to give an exact recommendation without knowing specifically what hardware you’re working with, but using a PSU Wattage Calculator, or determining the power draw of your different internal components and adding that together, can give insight into how many watts you need.
As a general rule, it’s better to err on the side of higher wattage rather than trying to match your needs exactly. If you’ve calculated that your system is going to use 500 watts (a common number for a straightforward gaming build), choosing a PSU with 600 or 650-watt output could be a good option, as it will give you some overhead to work with, and also allow for potential future upgrades.
Keep this in mind when considering higher wattage PSUs: a 750-watt power supply does not consume 750 watts by default. If your system is drawing 500 watts, your power supply will supply 500 watts, regardless of maximum capable output. Higher wattage output doesn’t necessarily mean more energy consumed; it means it has the ability to provide more power if your system demands it. That said, there’s no real advantage to having a vastly overpowered PSU if your system doesn’t need it, so you might be better served selecting a feature-rich, high-efficiency PSU that is closer to the wattage you require.
You’ll also want to consider the continuous power versus the peak power capabilities of your new PSU. Peak power is the maximum amount of power the PSU can output for short periods of time, whereas continuous power refers to the amount of power the PSU is designed to output on a regular basis. Peak power is usually reached when pushing your system to its limits, like when you’re running demanding games or performing hardware benchmarks.
If there is a sudden demand for more power, your PSU should be able to handle the higher output briefly, but should not be expected to run at those higher wattages continuously. Always make sure the PSU you purchase has sufficiently high continuous power output, and don’t choose solely by peak power capabilities.
As you'd expect from anything that deals with large amounts of power, system safety is a concern. A good power supply should have fail-safes built in — not just to protect the PSU itself, but also to keep your system safe in case of something unexpected, like a power surge.
The power supply and the motherboard are the only PC components that directly connect to almost every other piece of hardware in your system. Because of the unique position of the PSU in the PC’s layout, making sure it has built-in protection can help keep the rest of your hardware safe as well.
It’s worth noting whether the power supply you’re looking at has built-in protection, like OVP (Over Voltage Protection), which shuts down the PSU if excessive voltage is detected. Other safety features include functions like short circuit protection, which can be hugely beneficial if you encounter power fluctuations.
You’ll also want to plug in your PC to a surge protector. These hardware-saving devices are designed to add another layer of protection to your system by diverting potentially damaging power surges away from your valuable components.
Wattage is certainly an important consideration when choosing a desktop power supply, but so is PSU efficiency. Inefficient delivery leads to wasted power and more heat, which can potentially decrease the lifespan of your components.
Because this is such an important consideration, there’s a relatively straightforward independent rating system in place. You might have noticed the “80 Plus” rating on many power supplies, often listed alongside a precious metal. To receive this rating, a power supply must be at least 80 percent efficient, meaning that a maximum of 20 percent of power is lost as heat.
This efficiency rating is determined by performance in a 115-volt system, and the ratings are further increased as you go up the ladder of precious metals.
- 80 PLUS
- 80 PLUS Bronze
- 80 PLUS Silver
- 80 PLUS Gold
- 80 PLUS Platinum
- 80 PLUS Titanium
The more efficient your PSU, the less power it uses, and the less heat it generates. That said, higher efficiency usually means a higher price, so you’ll want to find the balance that works for you.
Even the most efficient PSU will still generate heat, however, and most use fans to disperse that heat. Many power supplies are designed so that the fan will only turn on when it needs to — that is, when the PSU hits a certain threshold. Features like these help to reduce noise.
For those who are interested in taking things to the very edge of practicality, there are even liquid-cooled power supplies for a truly silent experience.
Form Factor and Cabling Preferences
As with most PC hardware, there's a huge variety of options when it comes to what your power supply looks like.
One consideration when it comes to PSU form factor is the physical size of the unit. For the vast majority of desktop PC users, standard ATX power supplies should be fine, though you’ll still want to make sure your PSU will fit in your case by checking the appropriate clearances.
If you’re a small form factor PC (SFF) enthusiast, you’ll want to do a little more research to make sure your PSU will fit. There is a wide variety of SFF PSU sizes, like SFX, CFX, and more, so make sure you find the PSU that works with your case, no matter how small your PC.
Another important distinction when it comes to the physical attributes of your PSU is whether it’s modular or non-modular.
A power supply operates by converting energy from a wall socket and routing that power to each of the individual components in your system through a variety of cables. If your power supply is non-modular, these cables will already be soldered to the circuit board, meaning you don’t get to choose the cables that will be in your build. All the cabling, even the ones that you don’t use, will need to be stored in your case.
There’s nothing inherently wrong with this from a functional perspective, though poor cable management can lead to less efficient airflow, so you’ll want to be sure those extra cables don’t get in the way.
Modular power supplies, on the other hand, don’t come with the cables attached. This changes the installation process, as you’ll need to connect each cable to the PSU and the component that it is powering, but that also means you can optimize for fewer cables. This results in a cleaner build and potentially better airflow. Most people aren’t going to use every connector provided by the average power supply, which makes modular units a little more practical, as well.
There’s also a third, in-between option, creatively called a semi-modular power supply. These are exactly what they sound like: Some of the most frequently used cables are attached to the PSU, while some you’ll have to connect yourself.
For modular and semi-modular power systems, keep in mind that you do not want to mix and match cables from other manufacturers, or even different models from the same manufacturer, unless stated otherwise. Though the cable-ends that connect to the components in your build are standardized, the end that connects to the PSU isn’t, meaning different brands could have different connections. That’s why you should only use the cables that came with your power supply.
PC building is all about customization, and power supplies are no exception. In addition to everything we’ve discussed, there are a huge selection of additional features you can get from premium power supplies. Features like RGB lighting, additional connections, testing buttons, and power draw measurements via internal USB connections are luxuries more than necessities, but they are options if you’re interested.
An interesting aftermarket enhancement to consider is custom power supply cable sleeving. These custom cables allow the user to decide the color and material of their power cables, which adds a further level of customization to your build. This is purely aesthetic, but it’s another way to add some flair to a sometimes overlooked component.
Choosing your power supply should not be an afterthought.
Selecting the right one for your system should entail more than simply finding the highest amount of watts for the cheapest price. You need to consider form factor, efficiency, amperage, protection, and the cables you’re going to need, along with any other features you are looking for.
A good power supply can last for many years and can have a huge impact on the efficiency of your PC, so take the time to choose wisely.
Your PC will thank you for it.