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How to Choose a Power Supply for your PC

Updated: Sep 11, 2020

While the CPU and GPU may be the brains and the muscle of your computer, they wouldn’t get too far without any power. To be able to provide your PC with the energy it needs to run each of the components in the system, you need a power supply, otherwise known as a PSU (Power Supply Unit).

Power supplies can range broadly in price and quality, and, as is often the case with building a PC, you can be overwhelmed with the number of options on the table. If you’re a total noob, you’ll be left stranded. Let’s help you out by having a look at some of the important variables to choose from.

1. Power Output

The first decision you’ll need to make is around what level of output you’ll need your PSU to provide. The output of a PSU is measured in watts (W). In essence, this question is all about how much power does your particular PC need. How does one answer this question? Using mathematics of course! Don’t worry, it’s simple addition!


Take each of the components that make up your PC, and add the max power consumption for each. As an example:

  • CPU (95W)

  • GPU (450W)

  • RAM (5W)

  • Motherboard

  • WiFi adapter card (5W)

Total power consumption = 555W. In this example, you’d need a PSU that provides a minimum power output of greater than 555W.

Bear in mind however that having a 1000W PSU for a PC that only requires 500W will result in excess electricity costs with no benefits aside from having potential spare capacity for future upgrades. It is advisable to keep your PSU output close to your system input requirement so as to keep power costs low.

2. Efficiency Ratings

When it comes to supplying power to your PC, it goes without saying that you would seek the most efficient source of power at all times. Living in South Africa, this becomes even more relevant given the incidents of load shedding and the regular power surges as a consequence.

Efficiency is a measure of how well your PSU keeps your PC functioning as intended, using the lowest amount of electric energy. Efficiency is measured in terms of how much electric energy gets wasted via heat during operation of the PSU. For those who are interested, the efficiency of a PSU is its output power divided by its input power; the remaining input power is converted into heat. Here is the formula:

Output (in Watts) / Input (in Watts) = Efficiency (in %)

As an example, a 500W PSU (that’s the output) that requires 625W (from the wall, that’s the input), would be rated as 500/625 = 80%. The 125W difference would be wasted energy.

PSUs come in a variety of efficiency ratings. There is a certification program that rates different levels of efficiency into different tiers. This program is called 80 Plus. All 80 Plus certified PSUs operate with efficiencies of 80% and above, essentially meaning that 20% or less energy gets wasted through heat.

The rating tiers are as follows (from least efficient to most):

  • White (82-85%)

  • Bronze (85-88%)

  • Silver (87-90%)

  • Gold (89-92%)

  • Platinum (90-94%)

  • Titanium (94-96%)

More efficient PSUs cost considerably more than their less efficient counterparts. Any PSU that is 80 Plus rated will generally suffice for most purposes, but for gamers or persons using PCs for extended periods, a Silver or Gold PSU is recommended.

3. Heat and Noise

Now one of the things that is linked to the efficiency of a PSU is the amount of noise it makes. You’ll recall that we mentioned above that PSUs waste some percentage of energy via the generation of heat. This heat creates hot air inside your PC case. PSUs control the heat made by the unit by extracting the hot air out of the case using a large fan that resides within the PSU. The more heat the PSU generates, the more hot air will be produced and the faster the fan will need to run in order to effectively reduce the temperature in the case. What happens when a fan runs faster? It also runs louder.

Gamers, enthusiasts and even casual PC users will all agree - a loud PC is not desirable. Unless you are looking to use your PC for your Sunday braai or to heat up your house in the winter months, you’d do well to keep the heat (and consequently the sound) to a minimum.

How do you achieve this? Well, there are a couple of ways of looking at this.

  • Firstly, ensuring that you have an efficient PSU (see above) and that the PSU has sufficient output to power all your components (see above) is key.

  • Secondly, make sure that the airflow in your case is sufficient. This could mean having a number of other fans in your case that either pull cool air into the case, or exhaust hot air out. There are a number of cooling alternatives that can assist with this, but that is a whole different article.

4. Modularity

The next issue to consider is one of convenience. PSUs come in three variants - fully-modular, semi-modular and non-modular. You’ll see that PSUs have a number of cables coming from the unit. Modularity just refers to how the cables are managed. Anyone who has built a PC knows what a pain cable management can be. Cables can be facing the wrong way, too short, too long, too bulky, the list goes on.

  • Fully-modular: These PSUs have a cable management system that allows you to add or remove cables as needed. This is especially convenient for PC builders and those looking to optimise airflow in their case, as the cables that aren’t needed can be removed.

  • Semi-modular: These PSUs have a cable management system that allows you to remove some of the cables, but not all. This can be useful and is a sweet-spot between fully and non-modular variants.

  • Non-modular: These PSUs have the cables fixed in place to the unit. You are therefore stuck with the number and length of cables as provided by the manufacturer.

Semi and fully-modular PSUs cost more than non-modular ones, due to the convenience they provide. Look to get at least a semi-modular option if you’re trying to build your own PC. You will not regret the decision. If you’re putting together a budget build and you aren’t overly concerned about the innards of your PC, go for the non-modular ones.

5. Warranty

One last thing to consider is that PSUs have a habit of giving up, especially in a South African context where load shedding causes havoc with electronics. Make sure to look at the warranty provided by the manufacturer of the PSU. You’ll want a 3 year of greater warranty to ensure that any defects or unforeseen failures are covered. A 5 or even 10 year warranty is best, as this could cover future upgrades.

Important to note is that if you want to make use of the warranties provided by your chosen manufacturer, remember that sometimes they require you to register your purchase on their site soon after you receive it.


You are now fully equipped to purchase your PSU. Remember that there are a few RGB options too if you’re looking for a PSU that fits the overall case and PC design you’re looking for. Expect these to be more expensive though, of course.

Ready to make your choice? Head on over to our store and browse our hand-picked PSU options.

Looking for more ideas and advise around building your dream PC? Check out some of our other guides.