Power supplies: Often the least thought about, yet most important part of your PC. Why is it then, that most people buy the totally wrong PSU for their needs by going too small, or way too large?

Is it really that hard to choose a power supply that’s right for your system? Besides just wattage (which isn’t really that informative anyway), there are other considerations. Should you get a single rail or multi rail PSU? With cable management, or without?  What connectors do you need?

How would you know how much power your PC really needs? That’s the easy part. Simply fill in your specs on the online PSU calculator, add 100 watts for some headroom and Bob’s your mother’s brother. So, for the love of Doc Brown, why would someone who runs a 9600GT, 2.2Ghz C ore 2 Duo and 2 gigs DDR3 ram need a 700watt power supply? Really, now! The number of people who think they need a 1KW PSU is staggering.

You don't need a Mr Fusion to power an SLI setup

You don't need a Mr Fusion to power an SLI setup

Let’s look at a few examples. A basic system, Intel Core 2 Duo E4500, 4GB memory, P35 chipset motherboard, ATI Radeon HD 3650, an optical drive and one hard drive, needs around 90W of power at idle. Even at full load on the graphics card, processor, and optical drive, we still have a total power consumption of only 140W. Now, a mid-level system: AMD Phenom X4 9850 BE, 4GB memory, AMD 790X chipset, ATI Radeon HD 3870X2, an optical drive and two hard drives. At idle, with Cool & Quiet enabled, this system uses 168W, while it needs at most 341W  under full load. A high-end system: Intel Core 2 Extreme QX6850, 4GB memory, Nvidia 780i Chipset, Nvidia GeForce 8800 Ultra SLI, an optical drive and four hard drives. The idle power consumption for this setup is around 310W, and once we place full load on everything power consumption increases to 544W.

As I said earlier, wattage isn’t everything. Like LCD monitor response times and contrast ratios, it doesn’t mean much without context. The most important thing is the number of amps on the 12v rail(s). Combined, anywhere between 30 and 50 amps should be fine for your system. To be honest, if you choose a decent brand PSU, you shouldn’t have to worry too much about amperage. Antec, Seasonic, Zalman, Corsair and Enermax are all great PSU brands.

The Antec Neo He 550 watt is great value for money

The Antec Neo He 550 watt is great value for money

Some manufacturers use the peak rating of the PSU when classifying it. For example, the Gigabyte Superb 460 watt can only run at 460 watts for one minute. Its continuous rating is only 390 watts. The 585watt Odin is around 500 watts. Not all Gigabyte power supplies do this though. The Odin GT range is rated for continuous throughput. When you take this into account, it’s easy to see why the Odin GT 550 watt is double the price of the Odin 585 watt.

A decent PSU can be an investment, often outlasting every other component inside your pc.

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