ATX12v PSU Guide

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Apr 2, 2013
Last updated on 27th July 2013. Will be frequently updating this guide until I find it time to write a new one.
Hello Buddies and Builders ,
This guide is to solve those "Will my PSU be enough ?" or "Need PSU Help ?" questions on the forum. Before we get started , Please note that -
1. This is for standard or ATX12V PSU's. Please make sure you are looking for a ATX12V PSU. Even if you are not , Reading this tutorial might answer some of your questions.
2. This for new builders. If you are upgrading only the PSU from a old rig , This guide may not help you , Since older components have different ATX Versions.
3. Though every possible effort has been made to make this guide as descriptive and understandable as possible , It may not just help you to choose the right PSU. In that case , you may ask the forums or PM me.
4. This tutorial is written for voluntary purposes only. If you read this tutorial and follow the steps , you do so at your own risk. I don't hold any responsibility for any thing that may happen to your PC , or anything else due to mishandling , improper installation , wrong PSU purchase , etc.
5. Many other links have been given to various sites , e-retailers , other guides , etc. If you purchase from e-retailers , you do so at your own risk ( Don't get scared though , unless your Indian :p )
6. This guide isn't much technically detailed. If you want a detailed guide , on every component , this is the wrong place mate.
So lets begin.
//PSU Types
Some PSU's are sold alone , while some are given along with a case. Don't confuse them with a combo of a PSU and Case. Those which come with a case are good enough for a home or office PC and are a considerable choice for HTPC's. However for gaming PC's , I won't recommend them since these cheap PSU's under full load are likely to blast. Hence if your building a gaming PC you will have to choose a good gaming capable power supply.
There two ways to distinguish between PSU's -
By Certification
By Modularity

Lets start by distinguishing by certification - When you use a PSU , all the power isn't used , some of it goes waste. For example - If you use a PSU with 75% efficiency and rated for 250W , you draw and pay for 333W , If it has a 85% efficiency it would draw 293W power. The 80+ certification was therefore brought up. As the name says it certifies PSU's with a 80% Efficiency. There are four types of PSU's - Bronze , Silver , Gold and Platinum. Bronze has the least amongst thes four types while Platinum has the highest efficiency. For home user's 80+Bronze is enough. For gaming , it depends on setup , 80+Silver is good and 80+Gold for multi GPU setups.

Lets go to the Second type now , Modularity - These days , modular PSU's are becoming insanely popular. Wonder why ? because of their flexibility of cabling choices. Before I tell you more , lets see the three types of PSU's available depending on modularity - Non Modular , Semi-Modular and Fully Modular. Non Modular PSU's are PSU's which have all the cables attached to the PSU and can not be removed. Fully Modular PSU's are the opposite. These PSU's have ports on them. This allows the user to connect only the wires that are needed for the PC. This reduces the cluster of the wires inside the PC by alot. However these PSU's are more expensive compared to Semi or Non Modular PSU's. Semi Modular PSU's are the mixture of them. Some of the wires are not removable while some are modular. Modular PSU's have no advantage except the modular wiring when compared to Non Modular PSU's. Hence , this is the thing of luxury.

Selecting a PSU with the right wattage is one of the most important things while selecting a PSU. If you choose a PSU that is below the requirements of your PC , your PC won't turn on or may not function properly. However if you choose a PSU above wattage requirements above its need , it won't cause any harm. However PSU's with higher wattage cost more. In my opinion first plan whether you will upgrade your PC or not , if yes then how and how much wattage you will require , If you Overclock anything , etc. For example , If I choose a PC which has a maximum requirement of 630 watts and I plan to add a second GPU , which takes 170 Watts , I need a PSU of 800 W atleast. However I would go for 900W so If I add a bit more load , it will hold on. However in most scenarios , I recommend to buy a PSU with a wattage of 100-400W more power than needed for gaming ,and 50-100W for other PC's. This extra power will power your PC if you plan to add a custom water loop ,add in card ,etc. Even if not , get 100W more than required power. If you plan to have a GPU in your PC , always have a PSU to meet the minimum requirements specified by the manufacturer. In order to detect the required wattage check the manufacturers site or go to and select all the parts you have picked and see the estimated wattage. Buy a PSU with wattage higher than the maximum wattage.

Fans are another considerable thing. If you are a gamer , you must get a PSU with Fan. If you are buying a PSU for home or office use , a fan is not a necessity for you. But having one isn't bad either. Most modern high end PSUs have a Hybrid fan function. This means the fan won't spin until the PSU crosses a particular percent of load that is when it needs to spin in order to reduce temps. This is a smart function and is found in most Higher end PSUs. Nothing that should force you to get one though.

PFC (Power Factor Correction) is a technique that counteracts the unwanted effects of electric loads (reactive power) that make the power factor less than 1. The Power factor (PF) refers to the ratio of active power (measured in watts) to the apparent power (voltage multiplies current - volts x amps or VA), which includes both active and reactive power, and only active power is capable of doing work. For a power supply unit, the higher the PF value, the better it is able to convert current into useful power.

For residential and commercial users, only the active power is measured and charged (apparent power is measured and charged for industrial users), so the PF of the PSU does not directly affect your power bills in fact. However, PF does matter in the bigger picture, since the more reactive power there is, the less active power can be transferred - that is definitely a waste of power.

Power supply units without built-in PFC circuits often have low PF values, sometimes below 0.60. For PSUs with built-in PFC circuits, there are two types of PFC being used active and passive. Passive PFC consists of components that do not need power to work, for instance, ferrite core coils; and active PFC uses components such as integrated circuits and transistors, which do need power to work. Passive PFC can result in PF values between 0.60 ~ 0.80, while active PFC is able to deliver 0.95 ~ 0.99.

//Rails -
Rails are another important factor to consider while selecting PSU's. Here's a thread by hunter315 that will help you understand why rails are so important. Also note that PSU's with more than 900W on a single rail can be troublesome and dangerous at times. So I recommend getting a PSU with multiple rails if the wattage need is above 900W. Some PSU's like the EVGA SuperNova NEX 1500W offer adjustable amounts of rails. The users can adjust the number of rails to be used. These ofcourse have a limit though and are available in very expensive PSU's. The advantage is that you can have a separate rail for components like one for the CPU(s) , one for GPU(s) , one for the motherboard , one for the HDD/SSD(s) and one for other accessories. The disadvantage is that if you cross the max power limit on a particular rail , you will end up in a component(s) getting shutdown abruptly , causing damage to the component(s). But IMO this feature is only useful for extreme OCers and not for anyone else. So if your not in for some extreme OCing , opt for a single rail PSU.

//Some tips -
1. When buying a PSU , make sure it has all the plugs that your parts need.
2. Never connect a wrong pin in the wrong place , especially in a modular PSU. Doing so can cause harm to your PSU or Components. Check the user's guide and if necessary videos on youtube before installing a PSU.
3. If you hear any awkward sound from the PSU , immediately shut down the PC , unplug the main cord and open the PC and try to resolve the issue or get the unit RMAed.
4. Buy a PSU with a Mean Time Between Failure (MTBF) above 30,000Hours atleast. That way it is likely to last for 15,000 Days on a usage of 2Hrs a Day.
5. Buy a PSU with a voltage that your port provides. Most PSUs are universal but knowing this isn't bad either unless you want to be a victim of over voltage.
6. Check whether the PSUs length is supported by the Case you are buying.
7. Make sure your PSU has all the connectors you need for your system with adequate length. If not , get a 4 Pin Molex adaptor to the particular pin or a extension wire. But check whether the product supports that.
8. Make sure that the PSU you choose has a maximum power ( power which the PSU can give at its best with 100% stability ) of your requirements. Not the peak power. Else you will end up blowing everything or the PSU at least.
9. Make sure you use a good surge protector ( not a cheap power protector or power strip ) Also make sure that you don't use your PC during a thunderstorm or anything like that. ( Stupidest thing to do in such a case )

//Some other things you shouldn't really be bothered of
Digital Monitoring - Some PSUs ( like the Corsair AXi series ) support digital monitoring of the wattage drawn , PSU usage , load , etc. This is great for overclockers and pros. No gamer or other user should consider this as it is useless for average users.

//Haswell issues with PSUs
While many praised Haswell's low power capabilities , PSUs probably didn't.While the Ivy Bridge CPUs had a minimum power consumption of 0.5 A in a C6 or C7 state, the next generation of Haswell processors require only as little as 0.05 A, a 10x reduction. The problem is that a number of older or lower-quality power supplies are unable to deliver such low loads at stable voltages, meaning that the system could crash due to unstable voltages when in C6 or C7 state. However many companies have a list of compatible PSUs , amongst their existing PSUs. If you are opting for Haswell , you will probably need to check on this. There's a solution for this though , that is -
1. Boot the PC and enter its BIOS.
2. Go to the CPU settings page or whatever , that has the CPU settings.
3. Remove or disable the C6/C7 state.

This will make a Haswell CPU good to go with any PSU. Just remember you lose the low power advantage , though.

//Recommended PSU series ( as of 11th November 2013 )
For Home and Office users -
( All types ) Antec Earth-watts
Corsair Builder a.k.a CX

For Budget Gamers -
Antec High Current Gamer
Cooler Master GX
Corsair Builder Series a.k.a CX
Corsair Enthusiast a.k.a TX
Corsair Gaming Series a.k.a GS
Corsair Builder Series a.k.a CX
SeaSonic S12II
SeaSonic M12II
XFX ProSeries

For High End Gaming PC's and Higher end Builds -
Antec High Current Pro
( All types ) Cooler Master Silent Pro
Corsair AX and AXi
Corsair HX
Corsair RM
EVGA SuperNova
OCZ Fatal1ty
PC Power&Cooling Silencer Mk III
Rosewill Capstone 550W , 650W , 750W only
Rosewill Fortress
Rosewill Lightning
SeaSonic G Series
SeaSonic X Series ( Fan only )
SeaSonic Platinum Series ( Fan only )
Thermaltake Toughpower XT
XFX Pro Series
XFX XXX Series

Names mentioned above are of series. All models of that series are inclusive unless particular units are mentioned.
Please note that these series mentioned above are the ones I am aware of with a positive response. If you think I missed out a series please let me know. If any changes are made , the date on which they were made only for this one will be mentioned.
Recommended Brands -
Cooler Master
OCZ Technology

Other good brands -
OCZ Technology

All Apevia PSU's
All Apex PSU's
All Athena Power PSU's
All Azza PSU's
All Coolmax PSU's
All Diablotek PSU's
All Logisys PSU's
All Raidmax PSU's
All Sparkle PSU's
All StarTech PSU's
All TopPower PSU's
All VisionTek PSU's
All Xion PSU's
All Zebronics PSU's

//Updates will be made to this guides whenever necessary.
//Feel free to PM me for any suggestions or improvements you would like to suggest me for this or any other of my guides.
Sources - My brain.
Credits - Me , g-unit1111 ( suggested some links in the "Other guides/resources you might like" )

Other guides/resources you might like -
Proximon's PSU guide
thechief73's Collection of PSU info
Randomizer's PSU Guide and UPS info
Tom's 101 for PSU's
Know your OEM's and see how they make a difference
Using one low cost PSU or not recommended ? Here's what might happen
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