This Guide
This is a guide intended for anyone who would like to learn enough about computer power supplies to be able to choose one for themselves or others. The language will be as simple as possible but there is a Glossary.
Why?
There are many factors that must be considered when selecting a Power Supply Unit, or PSU for short. You may need one for a new system, or simply because you have heard about the dangers of owning a poor PSU. If you are reading this you probably understand that you want a safe PSU, one that won't fail and damage your components in the process. What you may not understand is the difficulty of diagnosing a PSU that has partly failed.
A poor or slightly damaged PSU can cause a system to display a wide range of symptoms which also resemble other issues. It can be almost impossible to diagnose a PSU problem at home without having another PSU to swap into a build. This is a very strong argument for getting a quality PSU... you need to have as much confidence as possible in this part because of the difficulties caused by a bad one.
What makes a good one?
There are several things to look for in a power supply, but the primary concern is the quality of power it produces. The power from your wall is way too energetic for delicate electronics, and that is why all of your electronics have some sort of power supply that converts the wall power to something useable. This is easy if you are powering one little device that has set needs. It gets a lot harder when you are powering a hungry device like a gaming computer that has very different power needs under variable circumstances.
So, your PSU has to be able to produce clean, adequate power while idling, and has to do the same under full load. But then it also has to do so at any level of power demand in its range.
When we say "clean and adequate power" we mean several things, and it starts to get technical. We can easily see one thing though, and that is that making a device that can supply 45W whenever asked is a lot easier than making a device that can supply 50W to 1200W and any number in between.
80plus - Some food for thought. This is a temporary link until I add a little more data and explanation.
http://www.hardocp.com/article/2011/10/04/80_plus_irrelevant_to_you_when_buying_psu/
If you would like to learn more about power supplies and what makes a good one, here are some links. Be warned, it's not something you'll pick up in 10 minutes.
Hardwaresecrets.com - Everything You Need to Know About Power Supplies
jonnyguru.com - Power Supply FAQ
TechSupportForum.com - Power supply information and selection
A list of all the ATX spec sheets
What wattage?
The total wattage of the PSU is not really the most important. Computer Power Supplies have several different voltages they produce, but the most important one is 12V. That's the type of power that you need most to power a modern computer. So, getting a "750W" power supply that only actually produces 600W of 12V power might not work out for you.
Please see the next post for a detailed description of how to read a PSU label. This will help you figure out how much actual 12V power that PSU can supply.
Almost all quality power supplies are capable of producing MOST of their rated wattage as 12V power. There are a few notable exceptions though.
Calculating total power needs
Here are a few links to help you determine how much power you will NEED in your computer:
Atomic MPC forum - Mark84's extensive graph showing power usage of almost any gaming GPU from the last several years.
As the GPU is the largest single load on your PSU, this table can take you a long ways in determining your needs.
Extreme Outervision power estimator This is the most used and best of these tools, but it uses wattage not 12V amps.
Once you figure out how much power you NEED, you still should determine how much you WANT. Opinions vary on this, and it's a good way to start an argument on the boards... but I will say this: Buy a quality PSU that will last you for many years and cover any eventuality you can reasonably predict.
Glossary
Here is a glossary of terms that may be used in connection with PSUs, here and elsewhere:
http://www.tomshardware.com/forum/279124-28-glossary-common-power-supply-terms
Now that you are armed with some basic knowledge, you might want to make up your own mind about which one to buy. Most websites, and indeed most so-called PSU reviewers lack the knowledge and the equipment to test power supplies correctly though. So where do you turn for expert reviews regarding power supplies?
Here are the top 3 websites that review PSUs
http://www.jonnyguru.com/
http://www.hardwaresecrets.com/
http://www.hardocp.com/
And here is a database of most power supply reviews from ALL the qualified PSU reviewers
http://www.realhardtechx.com/index_archivos/Page541.htm
A List of Recommended PSUs
Were you hoping we would just tell you which PSU to buy? No problem. We have that covered too, with a list of the most recommended PSUs. Please note that this is just a partial list based on frequency of recommendation and such. There are many, many more good PSUs.
http://www.tomshardware.com/forum/322966-28-list-recommended-psus#t2430472
Johnny Lucky, a long time contributor here, has also assembled this large list of PSUs that have reviewed well:
http://www.johnnylucky.org/power-supplies/psu-recommendations.html
As well, Johnny Lucky has assembled a list of known lemon PSUs:
http://www.johnnylucky.org/power-supplies/psu-lemon-list.html
If you have general questions about this guide, or suggestions for it, feel free to make them here. If you want specific help about your build or intended PSU, ask in a new thread please.
----------------------------
This is a guide intended for anyone who would like to learn enough about computer power supplies to be able to choose one for themselves or others. The language will be as simple as possible but there is a Glossary.
Why?
There are many factors that must be considered when selecting a Power Supply Unit, or PSU for short. You may need one for a new system, or simply because you have heard about the dangers of owning a poor PSU. If you are reading this you probably understand that you want a safe PSU, one that won't fail and damage your components in the process. What you may not understand is the difficulty of diagnosing a PSU that has partly failed.
A poor or slightly damaged PSU can cause a system to display a wide range of symptoms which also resemble other issues. It can be almost impossible to diagnose a PSU problem at home without having another PSU to swap into a build. This is a very strong argument for getting a quality PSU... you need to have as much confidence as possible in this part because of the difficulties caused by a bad one.
What makes a good one?
There are several things to look for in a power supply, but the primary concern is the quality of power it produces. The power from your wall is way too energetic for delicate electronics, and that is why all of your electronics have some sort of power supply that converts the wall power to something useable. This is easy if you are powering one little device that has set needs. It gets a lot harder when you are powering a hungry device like a gaming computer that has very different power needs under variable circumstances.
So, your PSU has to be able to produce clean, adequate power while idling, and has to do the same under full load. But then it also has to do so at any level of power demand in its range.
When we say "clean and adequate power" we mean several things, and it starts to get technical. We can easily see one thing though, and that is that making a device that can supply 45W whenever asked is a lot easier than making a device that can supply 50W to 1200W and any number in between.
80plus - Some food for thought. This is a temporary link until I add a little more data and explanation.
http://www.hardocp.com/article/2011/10/04/80_plus_irrelevant_to_you_when_buying_psu/
If you would like to learn more about power supplies and what makes a good one, here are some links. Be warned, it's not something you'll pick up in 10 minutes.
Hardwaresecrets.com - Everything You Need to Know About Power Supplies
jonnyguru.com - Power Supply FAQ
TechSupportForum.com - Power supply information and selection
A list of all the ATX spec sheets
What wattage?
The total wattage of the PSU is not really the most important. Computer Power Supplies have several different voltages they produce, but the most important one is 12V. That's the type of power that you need most to power a modern computer. So, getting a "750W" power supply that only actually produces 600W of 12V power might not work out for you.
Please see the next post for a detailed description of how to read a PSU label. This will help you figure out how much actual 12V power that PSU can supply.
Almost all quality power supplies are capable of producing MOST of their rated wattage as 12V power. There are a few notable exceptions though.
Calculating total power needs
Here are a few links to help you determine how much power you will NEED in your computer:
Atomic MPC forum - Mark84's extensive graph showing power usage of almost any gaming GPU from the last several years.
As the GPU is the largest single load on your PSU, this table can take you a long ways in determining your needs.
Extreme Outervision power estimator This is the most used and best of these tools, but it uses wattage not 12V amps.
Once you figure out how much power you NEED, you still should determine how much you WANT. Opinions vary on this, and it's a good way to start an argument on the boards... but I will say this: Buy a quality PSU that will last you for many years and cover any eventuality you can reasonably predict.
Glossary
Here is a glossary of terms that may be used in connection with PSUs, here and elsewhere:
http://www.tomshardware.com/forum/279124-28-glossary-common-power-supply-terms
Now that you are armed with some basic knowledge, you might want to make up your own mind about which one to buy. Most websites, and indeed most so-called PSU reviewers lack the knowledge and the equipment to test power supplies correctly though. So where do you turn for expert reviews regarding power supplies?
Here are the top 3 websites that review PSUs
http://www.jonnyguru.com/
http://www.hardwaresecrets.com/
http://www.hardocp.com/
And here is a database of most power supply reviews from ALL the qualified PSU reviewers
http://www.realhardtechx.com/index_archivos/Page541.htm
A List of Recommended PSUs
Were you hoping we would just tell you which PSU to buy? No problem. We have that covered too, with a list of the most recommended PSUs. Please note that this is just a partial list based on frequency of recommendation and such. There are many, many more good PSUs.
http://www.tomshardware.com/forum/322966-28-list-recommended-psus#t2430472
Johnny Lucky, a long time contributor here, has also assembled this large list of PSUs that have reviewed well:
http://www.johnnylucky.org/power-supplies/psu-recommendations.html
As well, Johnny Lucky has assembled a list of known lemon PSUs:
http://www.johnnylucky.org/power-supplies/psu-lemon-list.html
If you have general questions about this guide, or suggestions for it, feel free to make them here. If you want specific help about your build or intended PSU, ask in a new thread please.
----------------------------