A mistake seen too often by myself and other experienced computer builds is someone who’s trying to save a few dollars by getting a cheap power supply, only to hear from them later on about having troubles with their computer such as it not starting, freezing, random rebooting, or worse, having the power supply take down a few parts if not the entire computer system by blowing up.

The power supply is responsible for delivering constant stable power, preventing the current from fluctuating too much and protecting your computer from power surges and other electric dangers.

Skipping on your power supply only to save a few dollars is a recipe for disaster sooner or later.

In this article, I will give you detailed explanations on how to avoid 6 common mistakes when choosing a power supply.


  1. Buying a Power Supply that Cannot Deliver Enough Power
    1. How much power do I need?
  2. Buying a Power Supply that Cannot Deliver Enough Amps on the 12V Line
    1. Electricity 101: The Differences between Voltage, Current and Resistance.
    2. How does this apply to a Computer?
    3. Ok. Where’s the problem?
    4. Simple or Multiple 12V Lines (Rails)?
    5. How to find out the real total amount of Amperes that a power supply with multiple 12V Lines can actually deliver
    6. Confusing Marketing Tricks
  3. Choosing a no-name or low-quality brand power supply
    1. The difference between a no-name/low-quality and an high-quality power supply
    2. Detailed explanation of what is PFC
    3. The Watts Rating for a Computer may not be equal to the VA Rating.
    4. Brands to avoid
    5. My Top 10 Brands that I recommend
    6. What about this other brand?
  4. Not Considering the extra power requirements of Overclocking
  5. Not Considering How Many Connectors you Need Now and Not Planning Possible Parts Upgrades Down the road

    1. Making Sure You Have Enough Connectors for All Your Parts
    2. Planning Possible Parts Upgrades Down the Road
  6. A Power Supply with Poor Efficiency

    1. While your computer won’t explode due to a power supply with poor efficiency, your electric bill will!
    2. 80 PLUS Certified
  7. Bonus Point: The Best Power Supplies For Your Money

1. Buying a Power Supply that Cannot Deliver Enough Power

For your computer to function properly, your power supply has to be able to deliver enough power to your components. The number 1 point in this article is power, measured in Watts (W).

How much power do I need?

It’s impossible for me to give you a single answer, as everyone have different computer systems with different power requirements. However, if you’re building one of PC build featured on this website, I list the power requirements in the power supply section.

Alternatively, I recommend that you use the following power supply calculator:

eXtreme Power Supply Calculator

Enter the parts that you use, or intend to use and indicate whether you intend to overclock or not.

Add 100 Watts to your results

Once you have a number, I recommend that you add up 100W to your result.
For example, if you get 402W out of the eXtreme calculator, I’d recommend getting at least a 500W power supply.

Why? Because you don’t want your power supply to run too close to its maximum output, as that will shorten its lifespan, make it less efficient (costing you more on the electricity bill and generating more heat/noise). Also because the power supply calculator isn’t perfect and you rather want to be on the safe side with those much power than on the dangerous side with a power supply too close to its maximum capacity.

Keep in mind that overclocking increases your power requirements. l’ll go in details about this in point #4.

Alright Mathieu, I know how many Watts I need, can I buy this (Insert Number) Watts power supply from x brand?

No, not yet. Remember the title of this article? 6 Common Mistakes to Avoid when Choosing a Power Supply.

Watts are only the first point, you have five more mistakes to avoid. Now that you know how many Watts you need, let’s move on to point #2.

2- Buying a Power Supply that Cannot Deliver Enough Amps on the 12V line

As much as the power (Watts) requirement matters, the current requirement, measured in Amps is as important if not even more important. This is especially true if you have a or several dedicated video card(s). As a general rule of thumb, you’re aiming for the highest number on the 12V line.

What? Now I have Watts, Amps and 12V line?! This is way too confusing!

Fair enough. Let me explain this in plain English with a very simplified electricity 101 course:

Electricity 101: The Differences between Voltage, Current and Resistance.

Three of the most basic units in electricity are Voltage (Measured in Volts) and Current (Measured in Amps) and Resistance (Measured in ohms).

A neat analogy to help you understand these terms is a system of plumbing pipes. The voltage is equivalent to the water pressure, the current is equivalent to the flow rate, and the resistance is like the pipe size.

There is a basic equation in electrical engineering (I = V/r) that states how the three terms relate. It says that the current is equal to the voltage divided by the resistance.
Thanks to HowStuffWorks for the information. For more information on this, visit their article here.

How does this apply to a Computer?

For a computer system, you need enough power (Watts). Different components in a computer need different voltage, such as 3.3V, 5V and 12V, among others. For your system to work properly, your supply has to be able to deliver enough power flow, in Amps (Amps = Watts divided by Voltage) to every part.

Now, in the recent years, the demand on the 12V line, used for the Processor and Video Card(s) have been increasing as these parts have become more powerful and demanding more and more power.

Ok. Where’s the problem?

A lot of cheap or poorly designed power supplies will be able to deliver enough power (Watts) but not enough power flow (Amps) to the components for them to function properly, resulting in your computer not booting up, freezing, crashing, randomly restarting, etc.

This is why the Amps ratings are as important as the Watts rating on a power supply. You do not want to overlook that.

Single or Multiple 12v lines?

There’s also the debate about using a power supply with a single or multiple 12V lines.

How do you figure out which one of the two a particular model is?

See the following pictures, which I’ll use for a comparison at the same.

Both power supplies are rated for a maximum of 550W power output in total overall.

Antec BP550 Plus 550W, with multiple 12V rails.

LEPA B550-SA, with a single 12V rail.

Can you spot the difference? On the Antec model on top, you have multiple 12V rails, named +12V1, +12V2 and +12V3, the two first of which are for 22A and the third one which is equipped for 25A.

On the LEPA model at the bottom, you have a single 12V rail, simply named +12V, rated for 38A.

You’re probably telling yourself that the Antec model, on top, has more much potential, with 69A in total by combining the three 12V rails!

Not at all. See, the thing that the marketing folks don’t tell you is that each of those multiple rails can deliver up to 22A or 25A, but they cannot deliver it all at the same time.

How to find out the real total amount of Amps that a power supply with multiple 12V Lines can actually deliver:

A good trend that I’ve been seeing in the last few years is that manufacturers are actually starting to write how many Amps all the 12v lines can deliver together, like the example on the above.

How do I find the Amps rating if all I have is the maximum amount of Watts all the 12V lines can deliver together?

Simply divide the Watts rating by 12 to get the Amps rating, based on the following formula: Amps = Watts / Volts. In the example above, 444W divided by 12V gives you 37A.

The lesson here: Don’t get confused by multiple rails Amps ratings

In this case, 37A is very far from the 69A that you might have thought that you were getting in the first place, right? That’s only 53.5% of what you might have thought of getting in the place case! Imagine buying a car only to discover that it offers only 53.5% of the power than you thought, because of confusing marketing tricks. You would be pissed right?

So this goes to show you that you have to be careful with multiple 12V rails power supply for that. Marketing makes it look like this particular power supply from Antec does deliver up to 69A on the 12V lines, because anyone could easy conclude that by adding up the three 12V rails amps together.

3. Choosing a no-name or low-quality brand power supply

The differences between a no-name/low-quality and a high-quality power supply

A high-quality power supply is equipped with higher quality components that protects your computer from a variety of risks. It will also be equipped with safety circuitry to prevent damage resulting from short circuits, over current and over voltage.

A cheap or low-quality power supply may not be equipped with such safety features and will let your computer take the damage resulting from electric dangers!

Most important, high-quality power supplies can actually output the power that they are rated for.

Brands to avoid, except for specific models/series recommended below:

  • A-TOP Technology
  • Apevia
  • Aspire(Turbo Case)
  • Athena Power
  • Broadway Com Corp
  • Coolmax
  • Deer
  • Diablotek
  • Dynapower USA
  • Dynex
  • EagleTech
    FSP, other than the Aurum Gold series and the 400W 5.25″ drive PSU
  • HEC
  • Hiper Type-R
  • Huntkey
  • I-Star Computer Co. Ltd
  • In Win
  • Just PC
  • Linkworld Electronics
  • Logisys Computer
  • MGE
  • MSI
  • Norwood Micro/ CompUSA
  • NorthQ
  • OCZ
  • Okia
  • Powmax
  • Q-Tec
  • Raidmax
  • Rocketfish
  • Rosewill
  • SFC
  • Shuttle
  • Skyhawk
  • Spire Coolers
  • Star Micro
  • Thermaltake Purepower NP
  • Thermaltake Purepower RU
  • Thermaltake TR2  (and TR2-RX)
  • Ultra X-Connect
  • Ultra X2 >greater than 700 watt
  • Wintech
  • XION
  • YoungYear
  • Zebronics

My Top 10 Recommended Brands, in alphabetical order

  1. Antec: Antec: Avoid any EarthWatts models over 700W and the Basiq 500W though.
  2. Cooler Master: Avoid their eXtreme series.
  3. Corsair: Avoid the CX series.
  4. EnerMax
  5. PC Power and Cooling
  6. RoseWill: Only their Xtreme/RX series. Avoid other series.
  7. SeaSonic
  8. SevenTeam
  9. Silverstone
  10. Thermaltake: Only their Purepower and Toughpower series. Avoid other series.

Thanks to folks at EggXpert and their Tiered Power Supply List that has been of great help for this section.

4. Not Considering the Extra Power Requirements of Overclocking

Overclocking, or raising a part’s (CPU, Video Card, RAM) frequency beyond the manufacturer set frequency to gain extra performance, is a strain for a power supply. If you overclock, it is even more important to have a high-quality power supply that can handle the extra load.

As the frequency increase, so does the power consumed by the overclocked part. If you raise the voltage, the power consumption goes up even more, putting even more stress on your power supply. How much is hard to quantify, as every CPU and video card have different power requirements. However, it is not rare to see the power consumption go up by 50W, 100W, 150W or even more, depending on your computer setup.

I simply recommend that if you overclock, make sure that your power supply is powerful enough to handle the extra load. If you have a cheap power supply or are already close to its limit, do not overclock as you’re putting your power supply and possibly your computer on the line!

5. Not Considering How Many Connectors You Need Now and Not Planning Possible Parts Upgrades Down the Road

So, you know how many watts you need, you keep a close eye on the Amps rating, have chosen a good brand and have taken in consideration overclocking (or no overclocking).

Making Sure You Have Enough Connectors for All your Parts

Now, you have to make sure that you have enough connectors for everything and that they are long enough.
Every power supply comes with a 20+4 (or 24) pin ATX connector and a 4/8 pin 12V connector, that both connect in the motherboard.

Each video card will need either one or two 6-pin PCI-Express connector, one or two 8-pin or a mix of the two. Needless to say, if you have 2,3 or 4 video cards, make sure to get a power supply with enough connectors.

Then you have hard drives, optical drives that use either SATA or Molex 4-pin connectors and fans that use molex connectors. Once again, make sure you have enough connectors.

Planning Possible Parts Upgrades Down the Road

Knowing that a good power supply can last you easily five if not ten years, you want to think about possible upgrades to your computer system in the future, to make sure that your power supply can handle the load with that new part.

For example, if you choose to go with an on-board video card for now, but decide to upgrade to an high-end video card, which can easily draw 150-200W alone, you want to make sure to consider that when you’re planning your power supply purchase. Same thing goes if you plan to add a second video card in the future.

Otherwise, your computer won’t boot, will freeze, reboot randomly or in the worse case scenario, your power supply will give up with a bang, literally. In the process, it might fry one or several parts in your computer too. You wouldn’t be happy if your brand new $200 video card gets killed because of an inadequate power supply now, would you?

6. A Power Supply with Poor Efficiency

One of the power supply jobs is the convert current from AC (From the power outlet) to DC (what your computer parts use). This is not a perfect process and some energy is lost in the process, in the form of heat.

A power supply efficiency, on average, can be as low as 60% or as high as 92+%.

While your computer won’t explode due to a power supply with poor efficiency, your electric bill will!

Let’s do some maths here to compare a 70% efficient power supply and a 85% efficient one, two efficiency level commonly found in computer power supplies.

Let’s assume that your electricity cost is $0.15 per KW/h, that you use your computer ten hours per day and that it consumes on average 500W (High-end Gaming PC during gameplay for example).

A power supply with an efficiency of 70% will use about 710W to output 500W. while a power supply with an efficiency of 85% will use about 590W to output 500W, for a difference of 120W between 70% and 85% efficiency.

120W x 10 hours = 1200W per day. 1200W per day x 365 days = 438,000 Watts more per year.
Now, your bill is in KW, so 438,000 / 1000 = 438 KW.
Now, multiply the KW with the cost by KW/H 438 x $0.15 = $65.70

That’s the difference in cost for your electricity bill for one year. In this example, using a less expensive but less efficient power supply will cost $65.70 per year more compared to the power supply with 85% efficiency. Considering that you’ll have your PC for many years, you can quickly see the importance in investing in a more efficient power supply, as the higher cost for it will quickly pay for itself over time in lower electricity bills.

80 PLUS certified:

Power Supplies that are certified 80 PLUS have been independently tested for their efficiency. Now, there are 4 different 80 PLUS certifications, depending on how efficient the power supply is:

80 PLUS: The power supply is at least 80% efficient at 20%,50% and 100% load
80 PLUS Bronze: The power is at least 82% efficient at 20% and 100% and 85% efficient at 50% load.
80 PLUS Silver: The power is at least 85% efficient at 20% and 100% and 88% efficient at 50% load.
80 PLUS Gold: The power is at least 87% efficient at 20% and 100% and 90% efficient at 50% load.

The 80 PLUS and higher certifications are the way to go when you are looking for an efficient power supply.

Do not trust specifications such as “Efficiency: 80% to 85% Efficiency Typical” that are not 80PLUS certified. 80 PLUS is an independent standard test. No 80 PLUS and “Efficiency: 80% to 85% Efficiency Typical” means that it is 80% to 85% efficient, according to the manufacturer that is, using their own in-house test, which may or may not so much represent real efficiency.