How to Choose a Power supply?

By Rustam Iqbal | Last updated:

How to Choose a Power supply?

The power supply unit or PSU is responsible for providing all of your computer’s parts with the electrical energy they need to function. If you have a bad, outdated, or poorly rated power supply it could cause one or more of the following issues: not powering up at all, powering on and off repeatedly, not running compliant hardware/devices, damage to components surrounding it in your case (such as from too much heat), etc.

Important Power supply Specs

Size (Watts, Amps, Volts):

The most important factor to consider when choosing a Power Supply Unit (PSU) is its wattage. This can vary greatly depending on how many components you plan to build your system with so make sure your PSU has enough wattage. A typical PSU comes in at anywhere from 300 watts and can go up to 2000 watts or more.

Power supplies come with one of two main types of connectors: Square Connectors (ATX), Round Connectors (EPS). Your case will not only tell you the type of connector(s) it uses but also the maximum number of cables for each type of connector! Make sure all your cables can connect and don’t forget to double-check the wattage before purchasing all your computer parts.


The most common things to look out for when choosing a Power Supply Unit (PSU) are its efficiency and certifications. Efficiency is measured in % load efficiency which indicates how much energy it wastes under different loads. 100% efficient means it uses no extra power at all by converting each joule of energy into usable electrical output, 0% efficient means that all of the joules are wasted and none of it can be used as electrical output.

The higher the % load efficient rating, the better! This is important because every watt you don’t use isn’t turning into excess heat inside your system which can cause performance drops or damage to your components.

Most power supply units also come with a variety of certifications which you can usually find in the specifications section when choosing one. Certifications are like safety tests that ensure the PSU meets certain required standards and requirements to maintain peak performance and reliability for a long period without overheating or damaging any other parts of your system.  

You’ll want to check for 80+ certifications meaning it has at least 80% energy efficiency under different loads along with any other certifications the unit may have which is generally very safe to purchase!

Size & Form Factor:

The size, shape & form factor of your power supply will be an important factor if you plan on using a Mini ITX case/build. This is straightforward, make sure your PSU will fit.

Frequency & Voltage:

The frequency and voltage of your power supply will be an important factor if you plan on using a high-end graphics card(s), especially if it is not PCI Express (PCIe) x4.

You’ll also need to consider how many PCIe connectors are available on your GPU and then match that up against the PSU’s number of PCIe connectors. This will ensure a sufficient amount of power can be supplied to not overload or damage any components in your system.

The number of connectors is usually specified in the PSU specifications or on your GPU’s requirements page. This can sometimes get confusing so just make sure you match it up before purchasing any computer parts (GPUs, PSUs). 


Another factor that is added to certain power supplies and if preferred is to have a Semi-Modular power supply unit (PSU). A semi-modular PSU allows for less clutter by only including cables needed with your system rather than having excess cabling included which really won’t be necessary. If you do prefer this option then make sure it matches up with what your case has available for its build configuration!

Some common cables you’ll see are PSU cables, CPU connectors, PCI Express (PCIe) cables & SATA power connectors.

Just a quick note, if you’re going to use multiple graphics cards, make sure the PSU you choose has enough connectors to support all of them and if they need extra power supply units! Not doing this could result in overheating or damage to your components.

If it does not have enough connectors, consider getting a connector splitter that can convert one cable into two cables. It’s also important that the wattage of each graphic card is sufficiently high so as not to overload the PSUs’ capacity. The easiest way to do this is by checking for an 80+ certification meaning that it meets certain efficiency standards along with any other certifications the unit may have which is generally very safe to purchase!


The fan is one of the most important parts of a power supply unit (PSU) because it’s what keeps everything inside from overheating or thermal throttling. You’ll want to find a high-quality, well-known brand that has bearings that can be replaced vs. those with sleeve bearing fans which cannot usually be replaced and are only good for around 3-5 years before beginning to wear out.

Power supplies typically come with a 1x 90mm fan but you can upgrade to 2x 120mm fans instead if preferred for better airflow cooling performance in your build! I’d recommend finding a PSU with at least a 1x 12V connector as opposed to 4A since these deliver better overall performance than their counterparts during long periods while gaming or rendering.

Size & Number of Watts:

This is one of the most important factors to pay attention to, especially if you’re building a high-end gaming system where components tend to draw up a lot more power. Make sure your PSU has at least enough wattage (in Amps and/or in Watts) available for all your hardware needs!

This is especially true when it comes to overclocking which takes a lot of extra power because it’s essentially trying to gain performance from the system by overclocking or increasing the CPU operating frequency above its original default settings.

Ideally, I’d recommend having at least 30% more than what your entire build requires just so you have some wiggle room or headroom as well as not putting too much strain on a single component.

When it comes to choosing the best power supply for your needs, there’s always going to be some trade-offs and sacrifices so make sure you choose something that works best for your price range and size! Some PSUs are very compact and small but can’t deliver nearly as many watts or amps needed while others tend to be very large to accommodate for much more power delivery. 

Modular vs. Non-Modular:

This is a must when it comes to choosing the best power supply unit (PSU) unless you like having tons of unused cabling that will just clutter up your case as well as potentially limit airflow. 

If you don’t have the option for a semi-modular or modular power supply, then I’d recommend going in knowing which cables you’ll be needing and purchasing them separately so they can be easily swapped out without having any extra cables lying around.

There’s always some confusion on what exactly is needed but once again, look at either your motherboard, case, or diagram for reference! Some things to consider include cables for motherboard power connections, CPU power connections & PCI-E cables.

Wattage Rating:

This is going to be one of the most important factors when it comes to choosing your best power supply! If you’re building a high-end gaming PC, you’ll want something that can deliver its full wattage at all times without wavering and more importantly, consistently while not overloading or dropping below 90%.

This is especially true if you’re planning on overclocking as well since even slight fluctuations can cause damage to hardware if they get above 100% for too long which doesn’t happen very often but it can still be an issue depending on the power supply unit (PSU).

Being able to provide steady voltage over 10 years with consistent use is what’s most important with PSUs and you’ll want to look for something that has a very high total quality factor (QTF) when using synthetic load tests.

This means the PSU should be able to withstand and deliver its full wattage consistently for at least 10 years or 20000 hours while also having good voltage regulation, low ripple/noise, and excellent hold-up time under extremely cold conditions (-40C or below).


An important factor that is often overlooked in young builders’ purchases is the safety of a PSU. The safety approval label usually comes in 2 forms, with or without an additional sticker. Both are great so don’t be skeptical if your unit does not have this but keep this feature in mind as it’s not optional!

In some countries like New Zealand for example, units need to be certified by C-tick before being sold within their borders. Make sure it has either of these approvals before purchasing.

Ready to buy? Shop Power Supplies.

Rustam Iqbal avatar

Rustam Iqbal