Hands on: Choose the right power supply

It’s also important to check the conditions under which the manufacturer’s figures have been taken. Many budget models quote ratings at room temperatures or those within the PC case, but the power supply itself will normally be running much hotter. Power supplies don’t perform as well at higher temperatures, so beware of figures taken at around 25°C and instead look for ones under more typical conditions like 50°C.

Efficiency
So how many watts do you really need? A number of online calculators will provide an estimate, given the specifications of your system and your desire to overclock. Try Outer Vision’s Extreme calculator.

It’s also advisable to comfortably over-specify your power supply, not just to accommodate hungrier components in the future, but also because power supplies run at their most efficient when delivering considerably less than their maximum output. This means lower power bills, and cooler PCs with less waste as heat.

So if your components will draw a maximum of, say, 200W, don’t buy a 250W supply. Even assuming it could deliver sufficient power to the required rails, it would be running very inefficiently. Instead get a 350W or 400W supply and allow it to run more comfortably. A higher-rated power supply may be initially more expensive to buy, but it will be cheaper and cooler to run in the long term.

You may also notice some companies using an ‘80 Plus’ badge. This means the power supply conforms to the 80 Plus program which states a power supply must be at least 80 per cent efficient under various demands including full load.

Extras
Beyond power and efficiency ratings, you should also consider how quietly a power supply will run and the number and types of connectors it has. Modern PCs need a 24-pin motherboard connector, a supplemental four- or eight-pin plug for the processor and a six- or eight-pin plug for a PCI Express graphics card (or two if you’re using twin cards), along with the usual drive connectors.

Some may also allow you to detach any cables that aren’t required, for a tidier and more easily cooled PC.

As for models, Corsair, Enermax and Zalman consistently deliver good power supplies. All offer a wide range, but three budget models that are good value are Corsair’s VX450W, Enermax’s Pro82+ 385W and Zalman’s ZM360B, all for around £45. At those prices it really isn’t worth skimping on a poor supply.

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