# Computer Power Specifications – CompTIA A+ 220-801: 1.8

Each PC power supply lists a number of different specifications. In this video, you’ll learn how to interpret power supply specifications and how to avoid a voltage mismatch when connecting your computer to a new power source.

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As you start working with power supplies inside of your computer, there are a number of terms will come up that you need to know about. One of those is the amp. This is the ampere. You’ll also see this abbreviated with a capital “A.” This is the rate of electrons that can flow past a particular point in a single second.

If we were to actually clock this and watch all of the amps going through, it will be a total of 6.242 times 10 to the 18th power number of electrons flowing through a single point at a particular time. And we can say that that number happens to be one amp.

You’ll also see voltage referred to as a capital “V.” We often just call this a volt. That’s how much pressure is pushing those electrons through a particular circuit.

We often think about this as a hose and water flowing through the hose. If it’s a small amount of pressure, then it’s a lower voltage. If there’s a high amount of pressure going through, then the voltage is much higher.

Another important term that you’ll see is the watt. This wattage which is a calculation of volts times amps to come up with a total number of watts. This is the power that is used at any particular time.

So if we take that total number of volts, that pressure, plus how many electrons we expect to see go through a particular section and multiply those, we have a total number of watts. So 120V with 0.5A equals 60 W of power.

You’ll often see this written on your power supply itself. Here’s a label from a power supply. And if we go down the line and look at all these voltage and amps for the different rails, the different voltage rails of our power supply, you’ll see at the bottom this particular power supply allows you to have a total of 200W available to your system at any particular time.

When we start working with power, you’ll also notice there’s two different kinds of current that you’ll be working with. There is alternating current. And you’ll see this referred to as this wavy line, as we’re referring to power going through. That means that the direction of the power is constantly reversing. And you can see it goes from top to bottom and back again in a single cycle.

This is very efficient for sending power over very long distances. And that’s why in many places you’ll find that the power you’re connecting into on the wall is alternating current. The frequency of this cycle, as we can see here, is important to understand as well. In the United States and Canada, you’ll have connections coming out of the wall that are somewhere between 110 to 120V of alternating current. And this is running at a cycle of 60 cycles per second or 60 Hertz.

In other parts of the world, you may find 220 to 240V of alternating current coming right out of that connection on the wall. And it’s running at a different frequency. Its frequency is 50 Hertz.

You’ll also see power supplies refer to direct current. Direct current is usually what we’re taking from the AC power and we’re converting it in our power supply to direct current. Direct current is a constant voltage. It’s not changing direction constantly. And it’s very good to use when you’re looking for a type of current that’s very, very consistent.

So you can also see that DC is referred to with these straight lines, with these little connections along the bottom. We’re often taking this alternating current right out of the wall into our power supply. And then our power supply is converting it to direct current and then providing different voltages of direct current to the different voltage rails inside of your computer.

Parts of your computer will need 5V. Some parts of your computer will need 12V. And it’s the responsibility of your power supply to separate out and provide those different voltages to those different parts of your computer.

Now that we know these different terms and different symbols, let’s see if we can decipher what we might see on a power supply itself. If we look at this label, we can see that this power supply, the input to this power supply is expecting either a 100 to 120V of alternating current. You can see the little wave there. That is going to need about 4A to operate.

If we’re plugging into an international power connection, this particular power supply can also take 200 to 240V of power, again alternating current. And it takes in about 2A worth of power from that connection. And then it will output onto the inside of your computer a plus 5V, a plus 3.3V, a plus 12V, a minus 12V, a plus 5V, and a minus 5V of power across different rails.

Notice that power has the DC symbol next to it. So there’s the conversion where your power supply has taken AC power and is now providing DC power at different voltages throughout your computer. And depending on the different rails, it will be providing a different total amount of amperage as well.

Now, you can start doing calculations inside of your computer and determine how much power you’re going to need with these different voltages to make sure that this particular power supply can handle it. Because as you can see, the total output on the 5V and the 3.3V is configured to only get up to about 110W. It can’t handle much more than that. This is an older power supply. So if I needed more power than that, I need to get a completely different power supply and replace it inside of my computer.

The ATX power supply is a very standard shape and size. It’s so you can take out an existing power supply and simply replace it with another ATX power supply. And you know that it’s going to be compatible with what was there previously.

The power supply you’re using may have a lot of different connections that are hardwired directly into the power supply. You can’t change them out. There’s no modification. So when you’re buying the power supply, you have to make sure that you have the right kind of connectors for what you’re doing.

These days, you might also find power supplies that are completely modular. Here’s the same ATX type of power supply. But notice that the connections on the back allow you to plug in very standardized connections, depending on what you needed to have on the other end. That keeps down the number of cables that you would have inside of your computer. And it also lets you add and remove exactly the type of power connections that you might need.

As you get into smaller motherboards with a smaller cases, you may find smaller power supplies. This is a standardized power supply called a micro ATX because it’s a lot smaller than that standardized large ATX connection. So you may find different sizes. Make sure if you’re swapping out the power supply inside of your computer, that you get exactly the right size and you get one that’s going to fit into that case.

Some power supplies might have a switch on the back. There’s a physical switch, a physical connection on there that switches between 115V and 230V. So if you’re going from one location to another, across to different countries, you may want to make sure when you plug in this power supply, that particular switch is set exactly right.

If you aren’t certain exactly the type of voltage coming out of the wall, grab your multimeter, connect it to that wall socket, and see what type of voltage it registers. One thing you don’t want to do is that if there is a 230V power source and you’ve configured this for 115V and you powered in and plug it into that connection, it’s going to overload that power supply very, very quickly. It’s going to destroy that power supply. So make sure, if you’re connecting especially between different countries, check that little switch on the back and make sure it’s configured exactly right.

Some power supplies may not have a switch. And in that particular case, you need to make sure if that power supply is configured to only work on a certain voltage or if it is configured to be automatically switching between different voltages. If it’s one that’s been configured for a single voltage, you’ll probably see a note on the back that shows that this is alternating current of 230V at 50 Hertz.

It tells you this is exactly what I’m expecting. Do not give this particular power supply any other kind of voltage, at any other type of frequency.

If you’re plugging in a power supply and there’s nothing written on the back of the power supply, you might want to do some more research. This power supply for instance has a connection for the power. There’s a switch on the back. And then there’s no other text. There’s no other information on the back.

You may want to check the power supply. There may be something written on the top that says this is an autoswitching power supply and it doesn’t matter what type of voltage is coming in. It can handle anything. Or you might want to check the documentation to make sure that it is not a power supply that is expecting only a certain type of voltage.

As long as you’ve checked your documentation and you know exactly the type of voltage this power supply is expecting and you’ve used your meter to make sure that the voltage coming out of the wall will match one of those expectations, then this power supply should work just fine. And you want to be sure that all of those things are in place so that you can power up your computer successfully and safely.