Xoxide Resource Center: How to Buy a PC Power Supply

How to Buy a Power Supply

Author: Dave Melchiore

We encourage readers who find this information beneficial to share it with friends or other interested parties. Readers are encouraged to link to this article from their own websites.

Compatibility Connectors | Manufacturer Fibs | Power Supply Size
Modular and Sleeved Power Supplies | Recommendations

A power supply is arguably the most important component in every computer system. It must supply a steady, reliable source of power to every other component in the system, and it must do so without making too much heat or noise. If the power supply is incapable of providing the power needed, data corruption and possibly physical component damage could result. It is paramount, therefore, to choose a quality psu when building a computer.

Compatibility and Connectors

The most important feature of a computer power supply is its compatibility. A power supply's main connection is with the motherboard, and there are now two main standards for desktop computers that must be considered. Older and less feature-rich motherboards use the 20-pin ATX connector (fig 1.1). Newer, more feature-laden motherboards use the 24-pin ATX connector (fig 1.2). Although a 24 pin power supply can be used with a 20-pin motherboard via an adapter, it is not recommended to attempt the reverse, for a 20-pin power supply was not designed to provide the necessary voltage to all those wires.

Fig. 1.1 Fig. 1.2
20 Pin Connector 24 Pin Connector
20-Pin Connector 24-Pin Connector

In addition to main motherboard connectors, power supplies also differ in the other connections they offer. All power supplies have 12V molex connectors (fig 2.1) which are used to power peripherals such as CD/DVD-ROM drives, hard drives, and case fans. Make sure the power supply you are looking at offers enough molex connectors to meet all of your needs. In addition, the emergence of SATA hard drives and PCI-Express video cards means that you must make sure the power supply you are looking at provides these features if you plan on implementing them in your computer (fig 2.2 & 2.3).

Fig. 2.1 Fig. 2.2 Fig. 2.3
4 Pin Connector Serial ATA Connector PCI Express Connector
4-Pin Molex Connector Serial ATA Connector PCI-Express Connector

While on the topic of connectors, it is important to discuss the rails in a PSU. All computer power supplies have three voltage rails which they are responsible for regulating: the 3.3v rail, the 5v rail, and the 12v rail. The motherboard will draw current from these three rails in varying amounts, depending on the design. Current draw is difficult to find for most components, but if possible it is a good idea to research this and make sure that your proposed power supply will be capable of powering your system. Reputable power supplies have their maximum amperage ratings for each rail printed somewhere on the unit.

A new technology called SLI has recently surfaced in the computer industry. This revolutionary concept allows a user to combine the processing power and memory of two video cards, allowing for insane performance. If you plan on using dual video cards in your 1337 gaming rig, you need to make sure the power supply you purchase is SLI Certified if you have Nvidia video cards, or ATI CrossFire Ready if you are running ATI. This will ensure that the power supply is capable of feeding not one, but two hungry video cards, and will help reduce the possibility of instability.

Power Supply Connectors
Connector Use
20 or 24 Pin Connector* Motherboard
Four Pin Molex CD-ROM, Standard Hard Drive, Floppy Drive, Fans, Lights, Most Accessories
Serial ATA Connector Serial ATA Hard Drive**
PCI Express Connector Most newer Video Cards
* Adapters are available for converting 20 pins to 24 pins, and visa-versa
** A Serial ATA Power Adapter can be used to convert a four pin molex cable to a Serial ATA Power Connector

Manufacturer Fibs

Speaking of instability, it is time to address a most unfortunate fact. Power supplies are almost always overrated in their peak wattage number (which is the number most heavily advertised). There are really only a handful of brands out there that do not involve themselves in these games. These are the brands that I talk about towards the end of this article in the 'Recommendations' Section. If you are going to buy from a lesser known brand you will want to pick a power supply that seems like “overkill” simply to make sure you have adequate power. If you are building a brand new system, anything under 400 watts simply won't cut it. SLI, multiple hard drives/optical drives, case lighting, and especially overclocking significantly raise this number. A general rule of thumb is that one should purchase the nicest power supply he or she can afford. The power supply should be the highest priority when choosing components; if working with a set budget, invest in the power supply and compromise elsewhere.

Power Supply Size

Finally, the last parameter which must be considered when purchasing a power supply is whether it will fit in the enclosure you have planned. Most power supplies conform to the ATX specification, and will work in most cases as a result. Cases with a top-mounted blowhole fan should be checked for clearance with a proposed power supply; the depth of power supplies is not standardized and could vary enough to make clearance an issue. If you are going with a small form factor or micro ATX case, make sure you have selected an SFX/Micro ATX Power Supply.

Modular and Sleeved Power Supplies

After all of the necessary parameters have been considered, there are plenty of other options a consumer has at his or her disposal. Power supplies take up a fairly large portion of the space inside a case, and as such are very visible inside windowed cases. Of course, no one wants to look at ugly red and black wires everywhere, so there are a few different solutions to deal with this problem. A sleeved power supply features plastic sleeving (usually UV reactive) that surrounds the wire bundles and offers a much cleaner appearance. Modular power supplies (fig 3.1) actually sport wires which can be plugged and unplugged from the power supply unit, which means that a user only needs to install the cables he or she needs. Such modular cables are also sleeved for the ultimate aesthetic appeal. If noise is a concern, there are a number of silent power supplies which provide power without using any fans and therefore have no moving parts. Such a power supply will not be as powerful as a fan-cooled version, but to some the lack of noise is worth it.

Fig. 3.1 Fig. 3.2 Fig. 3.3
Modular Power Supply Standard Power Supply Unsleeved Wires
Modular Power Supply Standard Power Supply Unsleeved Wires


Finally, a newcomer to the power supply scene will be at a great disadvantage without knowing which companies' products can be trusted. Luckily, such knowledge is not a trade secret and I am happy to share my thoughts. There are a number of well-established brands which can be counted on for quality and reliability and here at Xoxide we carry a large line of computer power supplies. PC Power and Cooling offers the ultimate power supplies on the market, and customers will pay for the superlative performance with a superlative price. Hiper Group is a relative newcomer to the power supply industry but has had an enormous impact on the scene with its popular and powerful Type-R product line. Fortron Source is a less-known and less-flashy but extremely high-quality company which supplies many OEMs and is known best for its low prices, and therefore high value. SilverStone is also a newcomer to the scene, but has acquitted itself well with the 600W Strider Modular power supply. Other excellent choices include Hiper and Aerocool. As long as a power supply is selected properly, a power supply from any of these companies will provide a stable source of power for years to come.

Also, feel free to tab through our power supplies sections to find just the right power supply for your application. On our site you can find Quiet Power Supplies, 24 Pin Power Supplies, SLI Power Supplies, CrossFire Power Supplies, Modular Power Supplies, Micro ATX Power Supplies, and much more.

Recommended Brands:

We encourage readers who find this information beneficial to share it with friends or other interested parties. Readers ARE encouraged to link to this article from their own websites.

Copyright Xoxide Inc. 2005 - Copying informaiton from this page without proper credit,
in the form of a link, is strictly prohibited