Installing the new power supply

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Before you install the new power supply, take a look at the back of it. There should be a red switch right underneath the plug for the power chord. Be sure that this switch is set to the correct voltage. For example, if you live in the U.S. it should be set to 115V. Most of the time they are set correctly by default, but you don’t want to take any chances, so take the extra second and check to be safe.

Now carefully insert the power supply into the case and position it in the proper position. You’ll notice that the cutout for it is oddly shaped and that it only fits a certain way. Screw it in securely. Then look at the bundle of cables coming from the power supply. Figure out which string has what type of connectors on it. Identify the connectors and figure out the best way to use them.

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First connect the power connector for the motherboard. If you look closer at the bottom of the connector you’ll see that some of the 20 pins have different shapes. This prevents you from inserting it the wrong way. In addition, you’ll notice the clip on one side. The socket on the motherboard that receives this plug has a notch on one side where the clip goes. Another easy way to match it up the right way.

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Similar case with the power connectors for the drives. They both are uniquely shaped and only fit one way. The bigger one is for the hard drives, CD-ROM drives etc. and the smaller one is for the floppy drive. But since you had to unplug the old power supply connectors you’ll probably remember how they fit anyway. Go ahead and connect the appropriate power connectors to all the drives in your computer.

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As a last step take all the cables dangling around in your case, gather them in an orderly fashion and carefully tie them up with plastic zip ties. This will make working inside the case much easier in the future and optimize airflow as well. Now double-check all your connections, make sure you didn’t forget to hook up any of your drives, make sure the power supply is securely mounted, that no cables are dangling near any fans, that the power supply is set to the correct voltage, etc.

AT-Style Power Supplies And Power Switches

If you’re installing an AT-style power supply, you’ll notice that there is an extra cable that we haven’t mentioned yet. It is for the power switch. One of the differences between AT and ATX is that with AT-style cases the power button connects directly to the power supply to turn the power on and off. On ATX-style cases the power button connects to the motherboard instead.

The replacement AT-style power supply probably came with not only the cable to the power switch, but also had a new power switch attached to it. This will leave you with two choices:


  • Use the new switch – This means you have to remove the old switch and install the new one instead. While this is theoretically possible, it is a major pain in the butt, because old AT-style cases are usually a pain to work with. And replacing the power switch is no exception. 
  • Use the old switch – This means you leave the old switch in the case. If you look at the switch from inside the case, you’ll notice that it has four different colored wires that run to the power supply. Carefully write down what color wire connects to what pin, then simply pull the wires off each pin. After installing the new power supply, remove the new switch it came with and plug the four wires onto the pins of the original switch following the color coding you wrote down earlier.

Our recommendation: Go with the second option. Keep the old switch unless you have reason to suspect it’s bad and needs replacing. Using the old switch is a lot easier, and doesn’t require removal of the front bezel, trying to screw tiny screws into even tinier plastic holes at impossible angles.

All set? Then close ‘er up, plug in the power chord, push the power button and enjoy the quiet hum of your new power supply providing your computer with the juice of life!


– Alex –

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