Identifying the size of your PC’s power supply is really not a complicated ordeal.  There are various reasons why you might need to know how much power your computer uses.  Maybe you would like to upgrade another component in your machine or perhaps yours just bit the bullet and you need to order and install a replacement.  Whatever the reason, you can use a very simple and straightforward process to find out how big your power supply unit (PSU) is.  Let’s start with a short summary of what these metal boxes do for those who aren't familiar with them.

Umm...what exactly is a power supply?

A power supply is one of the many building blocks of a complete computer system.  It supplies power to everything component in your computer.  This includes the led indicator lights on the front, the switch that powers the computer on and off, and even those fans you might hear faintly humming along as you work at your desk.  Put simple, you cannot have a computer without a power supply because all of the hardware components get their energy source from the Power Supply Unit (PSU).

What you need to do

For many of the integral parts of PC’s, they can be identified with a software program that scans a machine and spits out its specifications.  Unfortunately, there is no software (that I’ve been able to find) that tells you the size of your power supply.  The only way to obtain the information is to open the case and look at it.  The good thing is that opening up the case is fairly simple.  It usually just involves loosening a few screws and a bit of prying, if necessary. 

You can read my other article on opening a computer case where I go into the process with a bit more detail.  If you are considering doing any kind of physical work on your pc, you should consider getting some tools for protection against electrostatic discharge.  ESD could cause major damage to your machine.  One great tool that is commonly used among pc technicians is an anti-static mat.  Now, once you get the case open you’ve already done almost all the work!

Check the Label on the Unit

Once you get the case opened up, finding the power supply unit is a cinch.  Just look for a large, square metallic box near the back of the case in either the top or bottom corner.  This is the power supply.  On its side there should be a label.  You will have to read through the fine print to find the wattage.  Here is an example of a label that shows you what you’re looking for exactly:

Typical Power Supply label

In this example the total output of the unit in watts is indicated by “OUTPUT: 350W”

You should go ahead and write this down and tuck it away for safekeeping so you don’t have to open the case again.  That way in the future should you need to know the size of your power supply you will already have it covered.