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Choosing The Right PC Power Supply

Do you know they say you should look after your heart to have a happier, healthier and longer life, the same is exactly true about your PSU. It is the beating power house of any system and just like your heart, you’d never want it to miss a beat – because when it does the whole harmonious anatomical ballet tends to turn into a blob of mush, usually showing classical symptoms of deadness.

The PSU is one of the most critical components in a build and can sometimes be overlooked or downplayed by a first time builder, but it is not a component you want to have fail on you, as it is likely to take out several of those lovely other parts you allocated the power supply budget to. So you might be thinking – I’ll just buy the most powerful PSU I can get my hands on and then I won’t have to worry about not having enough power – but this can be a common mistake, which not only leads to a very empty wallet, but also a system that will run with less efficiency than a build which has the right sized power supply.

So how do you choose the right PSU for your build? There are 4 points to keep in mind;

2. Amps on the +12V rails(s)
3. Required connectors for your other components
4. PSU Quality and 80+ efficiency rating

1. Watts

Every component in your build will draw a certain amount of watts from the PSU, with the most hungry part usually being the graphics card. It all depends on your build, but as a guide the link below lists all the graphics cards by their required watts and amps.  Some other factors can be taxing on the power supply; like overclocking, a water cooling setup and even the amount of hard drives installed.

(Also Read: Power Requirements For Your Graphics Card)

Depending on your needs, the list above gives a holistic figure for a system that doesn’t require a special amount of power – if you’re in doubt, you can always add 50-100W to the power supply for overclocking. There are also a bunch of PSU calculators out there that will take into account all areas of your build; from the amount of fans, the number of physical CPU’s, water cooling requirements and even bitcoin modules.

(Recommended: eXtreme Power Supply Calculator Pro)

2. Amps on the +12V Rail(s)

Watts define overall power. However, that is not the only requirement to keep the system with enough power, as all circuits need the required amps – or as my physics teacher always used to say, the amps are like the water pressure in a water pipe that determines the rate of flow. The list shows the required amps needed for each GPU (Also Read: Power Requirements For Your Graphics Card) on the PSU’s +12V rail.

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To figure out the amperage, take the Maximum Combined Wattage across the +12V rail(s) and divide that number by 12 – for instance, the power supply label above would read 648W / 12 = 54A.

The Antec TP-650C Power Supply is on a Multi-rail so it has two +12V rails that support a maximum of 30A. It doesn’t matter if the power supply is a Multi-rail or Single-rail design these days, and you shouldn’t make a purchase decision by the number of rails alone. Single vs Multi has been a hot topic for quite some time, and a lot of what is said about them can be a bit off the mark – what you will find is most modern Single-rail PSU’s act like Multi-rails and vice verse, most most Multi-rails act like Single-rail PSU’s.

(Also Read: Single vs Multi Rail Explained)

3. Required connectors for your other components

It has been many the bane of my life when you get all your parts in, lay them all out in front of you in their shiny antistatic bags, still feeling a little bit tipsy off the “new car smell” that only an unblemished, first time unboxing can give you – to find you have got the wrong connectors on the PSU, so infuriating! But no biggie right? It’s not like something’s broken or missing, and nothing a few converter adaptors won’t be able too fix.. It’s just why did this have to happen on build day.

Luckily, it’s pretty easy to avoid this happening to you, as there are only two connectors that need to be checked; one for your graphics card (Also Read: Power Requirements For Your Graphics Card) and the other is for your motherboard – note on GPU’s, to double check the specifications for a particular model, as some graphic card manufacturers will make changes to the reference design.

pci-e pins complete

The picture above shows two connectors for your graphics card, on the left is a 6-pin PCI-E and on the right is an 8-pin that can be either a 6-pin or an 8-pin PCI-E, also known as a 6+2-pin PCI-E. Some PSU’s come with a fixed 8-pin PCI-E instead, where all 8 pins are a fixed connector and can’t be used as a 6-pin PCI-E. The benefit of a 6+2-pin PCI-E, is it gives you the flexibility to turn one of your connectors into an 8-pin PCI-E or a 6-pin PCI-E – depending on your Graphics Cards requirements.

gtx 970 pins n thatThe graphics card pictured above requires an 8-pin and a 6-pin PCI-E – it is a MSI GTX 970 Gaming Edition, and like the MSI GTX 970 Gaming Lite Edition they require an 8×6-pin PCI-E configuration. However the MSI 970 Overclocked Edition requires a 6×6-pin PCI-E setup, and the MSI 970 Gaming Golden Edition only needs a single 8-pin PCI-E connection.

(See: Full Range of MSI GTX 970’s)

The Graphics card isn’t the only component that needs it’s own connectors; the DVD Drive, Hard Drive and Case Fans will need to be connected to the power supply by either SATA or Molex head connectors – and the motherboard needs two seperate power connectors to power the motherboard and the installed CPU.

mobo connectors complete

The picture above shows two connectors for your motherboard. The one on the left is a 24-pin, also known as a 20+4-pin, and plugs into both a 20-pin motherboard and a 24-pin motherboard – the one on the right is an 8-pin CPU connector that plugs into the motherboard to power the CPU, it can come in a 4+4-pin configuration to be compatible with just a 4-pin motherboard. Most modern PSU’s come with a 20+4-pin and a 4+4-pin connector.

4. PSU Quality and 80+ efficiency rating

Quality is better than quantity when comes to a PSU, you can have all the Watts and Amps in the world – but if it is a low quality PSU, then you are most likely going to destroy all your components when the power supply fails.

A good starting point to measure quality is the 80 Plus certificate awarded to PSU’s to denote their energy efficiency. Standard 80+ rating means the PSU is 80% efficient  under 50% load. A Gold 80+ rating would be more in line with 90% efficiency at 50% load – meaning it will lose about 10% of its energy to sound and heat. You can also get Platinum 80+ and even a Titanium 80+ rating, but the price of these power supplies usually outweigh the efficiency needed to most peoples builds.


Always buy your PSU from a reputable brand that states things like Maximum Combined Wattage, 80+ Rating, Amps on the +12V rails, over current protection, if they are being ambiguous with any detail, then pick a different manufacturer  – Notable brands include; Corsair, Cooler Master, XFX, Antec, be quiet!, Fractal Design, Zalman, Silverstone, to name a few.

Let me know in the comments if there is anything else you look for when choosing the right power supply for your build.

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