A power supply unit (or PSU) converts mains AC to low-voltage regulated DC power for the internal components of a computer. Modern personal computers universally use switched-mode power supplies. Some power supplies have a manual switch for selecting input voltage, while others automatically adapt to the mains voltage. At the time of budgeting for a custom PC, power supply price is one of the lowest cost to consider.
|Desktop Power Supply Price Comparison|
|Brand & Model||Price|
EVGA 500 W1, 80+ WHITE 500W, 3 Year Warranty, Power Supply 100-W1-0500-KR, Black
Thermaltake SMART 700W Continuous Power ATX 12V V2.3 / EPS 12V 80 PLUS Active PFC Power Supply PS-SPD-0700NPCWUS-W
Thermaltake Toughpower DPS G RGB 850W Digital 80+ Gold Smart Zero 256-Color RGB Fan Fully Modular ATX 12V 2.31/EPS 12V 2.92 Power Supply 10 YR Warranty PS-TPG-0850DPCGUS-R
Corsair RMx Series, RM850x, 850W, Fully Modular Power Supply, 80+ Gold Certified
Start From $130.00
Apevia ATX-BT550W Beast 550W High Performance ATX Gaming Power Supply, Low Noise, Supports Dual/Quad Core CPUs
Start From $23.00
Rosewill Glacier Series Continuous 80 Plus Bronze Certified Semi-Modular Design ATX12V/EPS12V 850W Power Supply Glacier 850M
Start From $84.00
YEECHUN 240W NEW Power Supply for Dell OptiPlex 390 790 960 990 3010 7010 9010 Small Form Factor SFF H240ES-00 D240ES-00 AC240AS-00 AC240ES-00 DPS-240WB L240AS-00 H240AS-00 3WN11 – 180 Days Warranty!
Cooler Master MWE 500 Watt 80 Plus Bronze certified power supply
A power supply is an internal hardware component that supplies components in a computer with power. The power supply converts a 110-115 or 220-230 volt alternating current (AC) into a steady low-voltage direct current (DC) usable by the computer and rated by the number of watts it generates.
Below is a list of parts you may find on the back of the power supply.
- A connection for the power cord to the computer.
- A fan opening to draw air out of the power supply.
- A red switch to change the power supply voltage.
- A rocker switch to turn the power supply on and off.
On the front of the power supply, which is not visible unless the computer is opened, you will find several cables. These cables connect to each the computer motherboard, and other internal components. A power supply connects to the motherboard using an ATX style connector and may have one or more of the following cables to connect power to other devices.
- Auxiliary connector
- Berg connector
- Molex connector
- P4 connector
What items are powered by the computer PSU?
Everything contained within the computer chassis is powered by the computer. For example, your motherboard, ram, CPU, hard drive, and disc drive are all drawing power from the power supply. Any other external devices and peripherals such as the computer monitor and printer have their own power source.
Note: If the computer is a laptop or an all-in-one computer the display may also be powered by the computer power supply.
The desktop computer power supply changes alternating current from a wall socket to low-voltage direct current to operate the processor and peripheral devices. Several direct-current voltages are required, and they must be regulated with some accuracy to provide stable operation of the computer. A power supply rail or voltage rail refers to a single voltage provided by a power supply unit (PSU). Although the term is generally used in electronic engineering, many people, especially computer enthusiasts, encounter it in the context of personal computer power supplies.
- Best power supply: Corsair RM750x
- Best budget power supply: EVGA 500 B1
- Best silent power supply: be quiet! Straight Power 10
- Best compact power supply: Silverstone SFX Series SST-SX550
- Perfect for Micro ATX and Mini ITX PC builds
- Best high capacity power supply: Corsair AX1500i
Power supplies are a frequently misunderstood—and overlooked—PC component. Many users choose a power supply based on total wattage alone, assuming that higher is always synonymous with better. Others pay no attention to their PSU selection at all, and settle for whatever abomination arrived with their machine. But considering how important a good power supply is to a system’s stability and long-term reliability, it’s a shame that PSUs get so little attention in comparison to sexier components like graphics cards and SSDs.
It doesn’t help that the power-supply market is awash with products from unscrupulous manufacturers that use substandard components and overstate the hardware’s capabilities. Indeed, the abundance of PSU-related misinformation and deception in the marketplace would be comical if it weren’t so harmful to consumers. But finding a solid, efficient power supply is possible if you arm yourself with the right knowledge. We can help.
Although ATX and ATX12V power supplies remain the same size, their main processor power rails and connectors differ. You therefore need to match these specifications to your PC’s requirements.
|Size||5.9 x 3.4 x 5.5 inches||5.9 × 3.4 × 5.5 inches|
|Primary Power Rail(s)||3.3V and 5V||12V|
ATX12V 1.0-1.2: 20-pin, 6-pin, and 4-pin
ATX12V 1.3: 20-pin, 15-pin 6-pin, and 4-pin
ATX12V 2.x: 24-pin
The 4-pin connector on ATX12V 1.x power supplies goes to the processor, the 6-pin connector to auxiliary components, the 15-pin connector on the ATX12V 1.3 supplies power to the SATA interface, and the 24-pin connector on ATX12V 2.x distributes power to your PC’s various components. You can also opt for micro ATX and mini ITX power supplies, which are smaller versions of ATX designed to fit smaller PC case.
Power Supply Unit Description
The power supply unit is mounted just inside the back of the computer case. If you follow the computer’s power cable, you’ll find that it attaches to the back of the power supply. It’s the backside that’s usually the only portion of the power supply that most people will ever see. There’s also a fan opening at the back of the power supply that sends air out the back of the computer case.
The side of the PSU facing outside the case has a male, three-pronged port that a power cable, connected to a power source, plugs into.
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|
|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
The most important distinguishable feature of computer power supplies is the form factor; this specifies the size, shape, and often other features of the device. The form factor must match the type of motherboard where the power supply is to be installed. There are a variety of computer motherboard styles and cases available, and typically each has a corresponding power supply form factor which should be chosen to match.
- ATX – Computer power supply designed specifically for the ATX motherboard. This is a motherboard designed by Intel to overcome the limitations of the AT motherboard specified by IBM. There are several modalities of this motherboard. The standard size of an ATX motherboard is 305 mm by 204 mm.
- Flex ATX – Power supply designed for an ATX variety with a size of 229 mm by 191 mm.
- Micro ATX – Power supply designed for an ATX variety with a size of 244 mm by 1244 mm.
- Mini ATX – Power supply designed for an ATX variety with a form factor of 150 mm by 150 mm size.
- AT – Power supply for the original AT motherboard designed by IBM with a size of 350 mm by 305 mm.
- LPX – Power supply designed for an LPX motherboard with a size of 330 mm by 229 mm.
- NLX – Power supply designed for an NLX motherboard with a size of 254 mm by 228 mm.
- SFX – Power supply designed for an SFX motherboard. The “regular” SFX power supply is nominally 100 mm wide, 125 mm deep, and 63.5 mm in height; it has an output of 90 W which is sufficient to run small systems with lower requirements and fewer peripherals.
Relating to form factor are the connections made by computer power supplies. Different connectors determine what devices power supplies can connect to and supply power for. It is important to select a power supply that has the right connections needed for the system.
Motherboard connector – connects the power supply to a particular motherboard. ATX motherboards are attached with 20 or 24 pin connectors.
CPU connector – used to connect power supplies to motherboards with on board computer processing units (CPUs). These are either 4 (“P4”) or 8 pin connectors.
Molex connector – the IDE connector that connects to hard drives and CD ROM drives. Most computer power supplies include at least one of these connectors.
Design tip: When additional Molex connectors are needed, a y-splitter can be purchased to increase the number of available connections.
Floppy connector – 4 pin connector used to supply power to floppy drives, card reader drives, and other similar devices.
AUX connector – a 6 pin connector that is a necessary connection for some computer motherboards.
SATA connector – connectors for devices using serial advanced technology attachment (SATA) interfaces, such as hard drives.
PCI express connector – used to connect to PCI express video cards, which receive power directly from the power supply rather than from the motherboard.
The important specifications of power supplies are directly related to their types and applications. However, the following are important specifications that pertain to all power supplies:
Input voltage is the magnitude and type of the voltage (in volts, V) applied to the power supply. This can be an AC or DC voltage.
Output current is the current (in amps, A) associated with the output voltage, typically given as a range or as minimum and maximum values. If the power supply produces more than one voltage (a multiple-channel power supply), for each output voltage there is a corresponding current that must be specified.
Output power is the power (in watts, W) delivered to the load. The rated power of the power supply must match the power requirements of the system, as an undersized device will cause power failure and computer rebooting. It is acceptable to use a power supply with an output power that exceeds the requirements of the application, as most are designed to step down to the amount of power demanded from them. This chart provides suggestions for power supply wattage based on computer system size:
Regulation indicates the stability of the output voltage. There are two types of regulation that can be specified when selecting a power supply:
Line regulation is the maximum steady-state amount that the output voltage changes as a result of a specified change in input line voltage. Line regulation is expressed as a percent change of output voltage caused by changes in the magnitude of the line (input) voltage.
Load regulation is the maximum steady-state amount that the output voltage changes as a result of a specified change in load. Typically, load regulation is expressed as a percent change of output voltage caused by increasing the load from half load to full load.
Operating temperature is the acceptable temperature range at which the power supply can function safely.
Features those may be important to consider for specific computer systems or applications beside the power supply price. Some of these features include:
- Fan cooling
- Heat sink cooling
- Over current
- Over voltage
- Power factor correction
- Remote On / Off switch
- Short circuit protection
- Standards and Compliance
For many applications, it is important that power supplies are compliant with certain organizational or national standards, such as these listed below:
- Restriction of Hazardous Substances (RoHS)
- Waste Electrical and Electronics Equipment Regulations (WEEE Regulations)