Computers, Laptops & Tablets Accessories & Hardware How to Install a Desktop Power Supply Swapping power supplies is straightfoward on desktop machines by Mark Kyrnin Writer Mark Kyrnin is a former Lifewire writer and computer networking and internet expert who also specializes in computer hardware. our editorial process LinkedIn Mark Kyrnin Updated on September 21, 2020 Accessories & Hardware The Quick Guide to Webcams Keyboards & Mice Monitors Cards HDD & SSD Printers & Scanners Raspberry Pi Tweet Share Email A power supply unit (PSU) converts the power from an electrical outlet into usable energy for a computer and its components. As the PSU supplies power and regulates overheating by controlling voltage, it is a crucial piece of hardware for any computer setup. In this guide, we show you how to install a basic computer power supply. Many name-brand manufacturer PCs use specially designed power supplies that have been built for their systems. As a result, it's generally not possible to buy a replacement power supply and install it into these systems. If your power supply has problems, contact the manufacturer for repairs or a replacement. How to Install a Power Supply Follow these steps to set up and install a basic power supply unit. Integrated PSUs—such as those in laptops and tablets—generally are not end-user replaceable. Take your laptop to a certified repair facility to replace a damaged PSU. Open the case. The method for opening the case varies depending on its design. Most new cases use either a panel or a door. Older computers require the whole cover to be removed. Remove any screws fastening the cover to the case and set the screws aside. All power supplies contain capacitors that retain power after the power supply is turned off. Never open or insert any metal objects into the vents of the power supply, as you risk electrical shock. Align the PSU in the case so that the four mounting holes align properly. Verify that any air-intake fan on the power supply faces toward the center of the case and not toward the case cover. Fasten the power supply. Hold the PSU in position while you screw it into the case. Set the voltage switch. Verify 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. Europe and other countries use 220/230v. Plug the power supply into the motherboard. If the computer has the motherboard installed into it, connect the power leads to the motherboard. Most modern motherboards use the large ATX power connector that is plugged into the socket on the motherboard. Some motherboards require an additional amount of power through a four-pin ATX12V connector. Connect power to the devices. Many items in a computer case require power from the power supply. Typically, these devices use the four-pin Molex style connector. Locate the appropriately sized power leads and plug the leads into any devices that require power. Replace the computer cover or return the panel to the case. Fasten the cover or panel with the screws that were removed when you opened the case. Plug in the power and turn on the computer. Plug in the power supply AC cord and turn the switch on the power supply to the ON position. The computer system should have available power and can be powered on.