Choosing A Computer Power Supply

Admittedly, power supplies or PSUs are not the most glamorous of components, however, they are one of the most important as without one your PC isn’t going to work.

Corsair 1500W AX1500i
Corsair 1500W AX1500i,

With that in mind there are a few things to take into consideration when choosing a power supply:


Different PCs require different output so it’s key to know exactly what sort of wattage your PC requires to operate.

Desktop power supplies typically range from 200 watts to 1800 watts (the latter being for ultra-high end builds) and it’s important to note that when choosing the power supply, you need to look for the sustained or continuous power output rather than ‘peak’ output.

Ideally, your power supply will be able to drive plenty of power to your components whilst still leaving some headroom. It’s advised to buy a power supply where you will only be using 50-60% of its capacity, this should leave you with room for expansion whilst achieving maximum efficiency.

Also, be aware of the myth that surrounds power output. It is not necessarily the case that higher-wattage power supplies consume more power.

Power Supply Efficiency Ratings

When choosing your power supply, be sure to check the efficiency rating before making a purchase.

80 Plus Energy Rating
80 Plus Energy Rating

In the world of power supplies, those with a higher efficiency rating tend to have better components, waste less power and generate less heat – all of which contribute to less fan noise.

A power supply with an energy efficient rating of 80 percent means that 80 percent of its rated wattage is used to power your system, whilst the other 20 percent is lost as heat.

You should most definitely be looking for power supply units bearing the ’80 Plus’ certification. The ’80 Plus’ certification system includes Bronze, Silver, Gold and Platinum. The power supplies with higher certifications often demand much higher prices. Average users will be ok with the simple 80 Plus or Bronze certified PSUs. If you’re building a high-end PC then we’d advise you to opt for a Silver or Gold certified power supply.

Single or Multi-Rail?

Manufacturers will specify the number of +12V rails their power supplies contain. ‘Single-rail’ PSUs have a single, high-power +12v for feeding power to hungry system components. ‘Multi-rail’ units divide their outputs between two or more +12V rails.

The design of a single-rail PSU means that all of the power will be available to any component connected to it. However, in the event of a failure the power supply has the potential to shoot much more current into the components.

Multi-rail PSUs main disadvantages are that they can’t share power among the different rails. For example, if you connect 256 amps worth of components to a +12V rail with a 20-amp maximum rating, the mismatch will trigger an overcurrent protection (OCP) mechanism and shut down. You must also pay attention to which components you’ve plugged in to which rail. Something you don’t have to worry about with a single-rail PSU.

However, disadvantages turn into advantages with a multi-rail PSU. Should you ever encounter a catastrophic failure, the multi-rails OCP mechanisms monitor each rail and will shut down the whole system should it detect an overload on any of the rails. The OCP kicks in much later on a single-rail PSU which could lead to a melt-down if a serious overload occurs.

So, which should you buy? We’d say that there are pro’s and con’s of both. If you’re looking for something that’s really easy to set up, then go for a single-rail unit. It you’re after that bit of extra security in the off chance that there is a serious overload, then we’d say you’re better off with a multi-rail.

Got any questions? Leave them in the comments section and we’ll get back to you as soon as we can.

Check out our full range of PSUs here. 


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