Installing a Desktop Power Supply

Close up of power supply being unplugged/plugged in to opened desktop computer


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This guide was developed to instruct readers on the proper procedures for installing a power supply unit (PSU) into a desktop computer case. It includes step-by-step instructions with photographs for the physical installation of the PSU into a computer case.

Many name brand manufacturer PCs use specially designed power supplies that have been built specifically for their systems. As a result, it is generally not possible to buy a replacement power supply and install it into these systems. If your power supply is having problems, you will likely need to contact the manufacturer for repairs.

All power supplies contain various capacitors inside of them that retain power even after the power supply had all power turned off. Never open up or insert any metal objects into the vents of the power supply as you can risk electrical shock.

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Opening the Case

To start with installing a power supply, it is necessary to open up the case. The method for opening the case will vary depending upon its design. Most new cases use either a panel or door while older systems require the whole cover be removed. Be sure to remove any screws fastening the cover to the case and set them aside.

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Aligning the Power Supply

Align the new PSU into place in the case so that the four mounting holes align properly. Make sure that any air intake fan on the power supply that resides in the case is facing towards the center of the case and not towards the case cover.

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Fasten the Power Supply

Now comes one of the most difficult portions of the power supply installation. The power supply needs to be held in place while it is fastened to the case with screws. If the case has a shelf ledge that the power supply sits on, it will be easier to balance.

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Set the Voltage Switch

Make sure that the voltage switch on the back of the power supply is set to the proper voltage level for your country. North America and Japan use 110/115v, while Europe and many other ​countries use 220/230v. In most cases, the switch will come preset to the voltage settings for your region.

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Plug the Power Supply to the Motherboard

If the computer already has the motherboard installed into it, the power leads from the power supply need to be plugged in. Most modern motherboards use the large ATX power connector that gets plugged into the socket on the motherboard. Some motherboards require an additional amount of power through a 4-pin ATX12V connector. Plug this in if required.

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Connect Power to Devices

A number of items reside within a computer case that require power from the power supply. The most common device is the various hard drives and CD/DVD drives. Typically these use the 4-pin molex style connector. Locate the appropriately sized power leads and plug them into any devices that require power.

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Close the Computer Case

At this point all of the installation and wiring should be completed with the power supply. Replace the computer cover or panel to the case. Fasten the cover or panel with the screws that were previously removed to open the case.

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Plug in the Power and Turn on the System

Now all that is left is to provide the power to the computer. Plug in the AC cord to the power supply and turn the switch on the power supply to the ON position. The computer system should have available power and can be powered on. If you are replacing an older or damaged power supply, the steps to remove the power supply are identical to installing them but in the reverse order.