The power supply guide

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In this guide I will explain to what a power supply does and why a good one is needed.

What is a PSU?

A PSU is short for Power Supply Unit. It is a box containing a transformer and is usually mounted inside your case towards the back. This is box that has the connector coming from it, going to the wall. Electricity supplied to your home is AC (Alternating Current). This cannot be used by the computer and as a result a transformer is used to convert it to Direct Current. The Voltage is also stepped down from 110V/240V to split Voltage rails inside the computer; +3.3V, +5V, +12V, which in turn power certain components within the system.

Power - Energy transferred per unit time. Power Supplies are advertised by the amount of Power it can deliver to the components. Units in Watts (W)

Voltage - Energy transferred per charge carrier. You may need to understand the importance of the 3.3V, 5V and 12V rails.

Current - The flow of electricity to components. Units in Amperes (A)

Efficiency - ((Power Drawn From Mains) / (Power Effectively Used)) * 100%
where > 75% is ideal.

What Determines a good PSU?

In short. One that's less susceptible to failure. Let's expand on that. What are the traits of a PSU that's susceptible to failure?

- Low Quality Internal Components. Difficult to judge as a consumer but sub $40/£30 price tag should ring alarm bells.

- Low Efficiency. This is infact a consequence of the above factor. The Conservation of Energy Law states that within a closed system, Energy (Power) cannot be created nor destroyed but are transferred in different forms. No Transformer can be 100% efficient. Inevitably, while some energy is transferred effectively as Electric Energy, some is transferred as heat or possibly sound. The latter two forms of energy transfer is effectively wasted or useless. A good PSU will waste less energy while a poor PSU will waste more energy. A PSU with a poor efficiency will always have to work harder to deliver the same power to the system components and this in turn can lead to failure.


A given system required 400W under load to function. We'll use a hypothetical PSU with a 80% efficiency and another with a 65% efficiency.

The first PSU needs to draw 400 / 0.8 = 500W from the Power Socket/Mains.
The second PSU needs to draw 400 / 0.65 = 615W from the Power Socket/Mains.

This in turn actually makes your system more expensive to run in terms of Electricity Bills

The above are factors that make PSU's more susceptible to failure.

 What Happens When A PSU Fails?

Sometimes a PSU shows symptoms of imminent failure. This may include system lockups, unexpected system restarts but also unexpected shut downs. More than often this occurs when the system is fully loaded, running a game or other intensive application. Eventually this can also happen when a system is just idling as a PSU continues to deteriorate. On the other hand, PSU failures can be imminent as well. In short, when PSU's fail there is a risk of it producing a surge effect that can damage or destroy other components within the system. Quite often the Motherboard is the first victim, followed by CPU, RAM and Disk Drives. This tends not to happen with well built PSU's.

Trusted PSU Vendor List

Fortron Source
PC Power & Cooling

Avoid List

Silver Power

My advice would be to choose a power supply from the below selection. I have missed some brands, so read about it before you buy it!
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