How To Guide 4Windows

How to Install or Replace a Computer Power Supply

Power supply is a vital component of a typical computer system that should be given importance just like other major computer components. Power supply powers everything inside the computer from motherboard to peripheral devices and other components inside the computer such as hard disk, optical drive, floppy disk, fan and also other component connected outside the computer such as flash drives or external drives that don’t have power connector but a usb cable attached to the computer. Computer power supply sits at top or at the bottom inside the computer case it is a metal box that has many connectors that connects to the motherboard and peripheral devices inside your computer. A cheap “generic” power supply will power your computer and it will work just fine with your system as long as you don’t have a high end motherboard, high end video card and don’t overclock your system, otherwise you’ll be facing many stability issues such as your computer won’t boot, the blue screen of death, constant freezing or system hang and recurring system reset.

Changing or replacing your power supply is not just a matter of replacing your old power supply with a power supply with a higher wattage. Things to consider when purchasing a power supply, first thing to consider is the PSU +12v rail with the maximum ampere indicated (e.g +12V 28A) the higher the ampere the better. Why is the +12v rail very important to consider when buying a power supply? Because the +12v will power most of the peripheral devices inside the computer including the microprocessor, that’s why it require a higher power rating also a good power supply has more than one +12v rail. Other thing to consider is the 20/24 pin and ATX 4 pin newer motherboard or high end motherboard uses 20/24 pin and ATX 8 pin motherboard power connector instead of the ATX 4 pin motherboard power connector, check your motherboard manual for more info on this. If you are using a high end graphics card this cards usually need a 6pin PCI-E power connector to boot so be sure to have this if you have a high end video graphics card.


  1. Be sure to choose the right power supply for your system check out power supply calculator for your system wattage requirement.
  2. If you are replacing your power supply unit, open your PC case, there are usually two screws at the back of your pc unscrew it and set aside the screw. Some pc case don’t use screws, instead you have to slide the cover to open, refer to your pc case manual on how to remove the cover of your pc.
  3. Locate where to mount the power supply it can be at the top or at the bottom of the computer case depending on the type of casing you have. In the image below the power supply is located above, some newer computer casing have their power supply mounted at the bottom.
  4. Disconnect all of the wires from the motherboard, hard drive, optical drives and any other that connects to the power supply then remove the power supply by unscrewing the 4 screws that hold the power supply and then insert the new power supply.
  5. Secure the new power supply by screwing it with 4 screws at the back of your casing, before screwing make sure you can see all screw holes of the power supply to avoid screwing the power supply on the wrong way.
  6. Plug-in the 20/24 pin power connector to the motherboard, old motherboard use 20 pin connector, you can easily remove the 4pin on the 20/24 pin connector by just sliding out the extra 4pin.
  7. Plug in the ATX12v power connector on the motherboard, this ATX12v is used to power the processor, high end motherboard use 8pin connector to power the processor. Don’t forget to connect the ATX12v on the motherboard otherwise your computer will not boot or the display screen will be blank.
  8. If you use floppy disk connect the floppy disk power connector to the floppy disk
  9. Locate the 4 pin molex connector and connect to the hard drive, optical drive or fans. If you are using SATA drives use the SATA power connector and plug it in on your SATA hard drives or optical drives. Some hard drives have both the SATA and Molex connector available so you can use either the SATA or the Molex connector but not both just select one of them.
  10. If you are using a mid or high end video card connect the 6 pins or 8 pins PCI-e connector on you video card, if you are using dual video card you need 2 x 6+2 PCI-E power connector one for each video graphics card.


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