What is a Power Supply Voltage Switch?

The power supply voltage switch, sometimes called the voltage selector switch, is a small switch located on the back of most desktop computer power supply units (PSUs)

This small switch is used to set the input voltage to the power supply to either 110v/115v or 220v/230v. In other words, it's telling the power supply how much power is coming from the power source.

What is the Correct Power Supply Voltage?
There isn't a single answer to which voltage setting you should use because it's determined by the country where the power supply will be used.

Check the Foreign Electricity Guide by Voltage Valet for more information on what voltage to set your power supply voltage switch to.

For example, if you live in the United States, the power supply voltage switch on your computer's power supply should be set to 110/115. However, if in, say, France, you should use the 220v/230v setting.

Important Facts About Power Supply Voltage
The power supply can only use what's being provided by the power source. So, if the outlet is transferring 220v of power but the PSU is set to 110v, it will think the voltage is lower than it actually is, which can cause damage to the computer's components.

However, the opposite is true too - if the power supply is set to 220v even though the incoming power is a mere 110v, the system may not even start because it's expecting more power.

Again, just use the Voltage Valet link above to find out what you should have the power supply voltage set to.

If the power supply voltage switch is incorrectly set, shutdown the computer and then switch off the power button on the back of the power supply. Unplug the power cable completely, wait a minute or two, and then toggle the voltage switch to its correct place before turning the power supply back on and reattaching the power cable.

Given that you're reading about changing the power supply voltage, it's likely that you're using your computer in different country. Since you can't use a power supply without a power cable, remember that it's probably true that you need a plug adapter in order to conform to the plug of the power source.

For example, the a NEMA 5-15 IEC 320 C13 power cable plugs into a regular North American flat pin outlet, but can't attach to a European wall outlet that uses pinholes. For such a conversion, you could use a power plug adapter, like this one from Ckitze.

Why Doesn't My Power Supply Have a Voltage Switch?
Some power supplies do not have a manual power supply voltage switch. These power supplies either automatically detect the input voltage and set it themselves, or they can only work under a specific voltage range (which is usually indicated on a label on the power supply unit).

Important: Don't just assume that because you don't see a power supply voltage switch, that the unit can automatically adjust itself. Like I just said, it's very possible that your power supply is only meant to be used with specific voltage. However, these types of power supplies are usually only seen in Europe.

More on Power Supply Voltage Switches
You can install a power supply by opening the computer case. However, some parts of it, including the voltage switch and power switch, are accessible through the back of the computer case.

Most power supply voltage switches are red in color, as in the example on this page. It may be located between the on/off button and the power cable, but if not, then somewhere in that general area.

If switching the power supply voltage setting is too difficult with your fingers, use something hard like a pen to change the direction.