You’ll need a power supply that’s powerful enough and stable enough to power all of the components in your system.
The power supply converts the electricity from your wall socket into a low-voltage, direct-current (DC) form that can be used by all the components that make up your computer.
Each hardware component may require several different DC voltages. A power supply is equipped to provide the required voltages via cables which simply plug directly into the parts (motherboard, graphics card, etc.).
Primary Selection Considerations
Most commonly available power supply units are compatible for many computer builds, so at a basic level the main factors to consider are:
Electrical Size (Wattage)
The overall wattage of the PSU must be large enough to supply all your chosen components reliably. Use a power supply calculator to get an estimate on your requirements such as http://outervision.com/power-supply-calculator.
Quality & Efficiency
Power supply quality can widely vary between brands and models. Choose a power supply from a reputable brand such as SeaSonic, Silverstone, EVGA, ThermalTake, Corsair etc and ensure the unit comes with adequate warranty.
Most importantly, look for the power supply’s 80 PLUS certification. This certification rates the power supply to a certain efficiency level – A more efficient supply means less energy wasted in the form of heat. 80 Plus Bronze and Silver are suitable for most systems however Gold, Platinum and Titanium exist. While these certifications rate efficiency, most units that achieve these certifications are also of high quality.
Physical Size (Form Factor)
Most custom PCs use a full ATX size power supply. This is the most common size / standard of a power supply and will fit in full ATX and micro ATX cases. Smaller power supplies can be found in smaller sized PCs such as mass produced PCs from Dell, HP etc and some smaller media center PCs.
While most high quality power supplies come with all the connectors you need, it’s worth checking the suitability to your particular build. If you’re running multiple graphics cards for example, you should check the power supply has enough PCIe 6 or 8 pin connectors to avoid the use of converters.
You may also wish to choose a power supply with modular cabling. This means that you can simply unplug the unneeded cables from the power supply to tidy up your case.
Secondary Selection Considerations
If you wish to choose your power supply with a little more detail, you could also consider the following features:
Noisy fans or ‘coil whine’ from a low-quality PSU can be an annoyance that you will probably wish to avoid.
Refers to the stability of the output voltages which are supplying your computer parts, and how close to the nominal volts these will stay in practice when the PSU is under load.
PSUs convert sinusoidal alternating current (AC) waveforms to flat direct current (DC) waveforms. A low ripple voltage is desirable as it means the output closely resembles a flat waveform.
Not generally a concern unless building high-end systems with multiple graphics cards. Basically, your power supply must have sufficient ‘juice’ to be able to supply all of your chosen hardware components at once on each power rail. Power supplies with multiple power rails typically balance their connectors across each rail to evenly distribute the load – this is where using molex to pcie converters for graphics cards can potentially cause problems. Choosing a power supply with a large single 12 volt rail instead of multiple 12 volt rails can simplify the selection process in this scenario but it’s always preferable to choose a power supply with the correct connectors and avoid adapters.
Heat is generated as an unintentional by-product of converting power from one form to another. It can decrease the performance of your computer hardware and damage components if not controlled to acceptable limits. Most PSUs contain fans for heat management, though the fan direction may be a consideration on some models.
Color and style
If aesthetics are important in your build, you may wish to consider the appearance of your PSU.