Whether you are purchasing a power supply for your new computer or just replacing an old one we hope this will help in the selection process. If you’re replacing a power supply for Compaq, Dell, Gateway, HP, etc you may find it tricky as some of these systems do not accept standard PSU’s. We carry a large selection of refurbished and new PSU’s for these systems at our South Clerk St store should you wish to check if we have what you need then feel free to call on 0131 6629955.

What does “ATX” stand for? ATX stands for Advanced Technology eXtended. In summary it defines a set of standards in measurements and forms that helps make things such as computer power supplies interchange with one another. Due to this standard the majority of PSU’s that you are likely to come across will be ATX. There are variations however such as micro and mini ATX which as the names suggest are smaller than standard.

The first question to ask yourself is, “Is my power supply an ATX form factor?” (there’s a good chance it will be if you have a standard size PC) . If you have this information available then the selection process is much easier. The information is sometimes stamped somewhere on the power supply or may be contained in the manual for your existing computer. If you’re looking for an ATX power supply make sure the power supply is an ATX form factor, not micro ATX or any other.

Perhaps the most common method used in selecting a power supply is buying the largest wattage for the cheapest price. Certainly this makes,  say, and 800watt PSU at £50 look far more appealing than a 600watt for £80. But why the large gap in price Vs output? Simply put if you are looking at a PSU over 500watt and the price is under £50 there is a good chance the internals will be generic configuration from china with a brand label stuck on the outer casing.

While these power supplies may well do the job we would recommend something more solid such as Enermax or Corsair. These power supplies have built in surge protection, high quality Japanese capacitors and a low ripple on their outputs which means a cleaner and more consistent supply. They generally come with a warranty of 2-5 years depending on model, which is far and above the standard 1 year most manufactures offer.

You will also need to know how much power you’re going to need. It’s okay to buy a power supply that is larger than necessary because the power supply will step down to your power requirements. Power supplies typically deliver only the amount of power demanded from them. On the other hand, buying a power supply that is too small for your requirements can cause the power supply to burn out or fluctuate which can cause random errors or even damage hardware. If you are unsure of the wattage of the PSU you require then it would be best to call our staff who can advise you directly, however a typical value for an average home PC system would be in the range of 4-500watts.

If you are looking for a particularly high end power supply then most these days will have a bronze, silver or gold efficiency rating also. This means that they have a low wastage of electricity from the internal transformer and are most likely of a high build quality.

After you have chosen your wattage of power supply you need to take a look at what connectors you need. Different power supplies have different connectors so it’s best to choose one with connectors that meet your every need. It’s okay if you buy a power supply and not use some of the connectors. You can just leave them hanging unconnected but we would recommend having them neatly secured away from any fans or internal components. Also you can use cable splitters to create additional connectors but it is best to avoid this and use only the ones on the power supply itself.

A typical power supply will have a 20/24 pin ATX motherboard connector, 12volt connector, 3-4 SATA connectors and a couple of molex connectors. Higher end PSU’s will usually have 1-2 PCI-e connectors for graphics cards and an additional 12volt connector for higher grade motherboards also. Some are even modular meaning that you only have to have the connectors you are going to use plugged into it. This helps avoid unneeded space being used within your computer case and also looks neater in systems where you perhaps have a side window.

Generally speaking you want to go for a good brand such as  Enermax, Seasonic and a few others. These companies not only design the power supplies themselves but also manufacture them in-house to high standards. They also license their products to others such as Corsair, and EZcool. So while perhaps not well known for power supplies these companies also have high quality products.

So the next time you are considering a new PC and question why something as generic as a power supply may be double or even triple the £20 you may have seen in some shops, ask yourself this easy question. Do I really want to risk a £20 power supply which provides power to the £600+ PC I’m about to buy? Personally its an easy call.

For a range of psu’s please visit or call either of our shops for an up to date stock list.

South Clerk St: 0131 6629955     Inverleith Row: 0131 5523493


Author: Alexander Wright

Posted in Custom PC and tagged , .

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