Buying a Power Supply: Wattage, Efficiency and More

Buying a Power Supply: Wattage, Efficiency and More

Once you’ve chosen every other component in your computer, it’s typically time to select a PSU, or power supply unit. (Unless you’re just replacing one you already have.)

Last but certainly not least, the PSU is one of the most important components in your computer. In this article we’ll be discussing how to pick the best power supply for your needs.

The main things that distinguish power supplies from one another are, as follows:

  • Wattage: This is the amount of power the PSU will consume from your wall outlet and provide to your components.
  • Efficiency Rating: This is a rating showing how efficient the power supply is with its energy consumption. The higher the efficiency, the higher the quality of the power supply and the less power it’ll use. (Unless, of course, you’re using a high-wattage power supply and maxing it out.)
  • Modularity: Non-Modular, Semi-Modular and Modular. You’ll hear these words tossed around a lot where power supplies are concerned, and they deal mainly with cable management. I’ll get more into that one later.
  • Brand: This is actually super important; you want to buy PSUs from only the most reputable brands.

With that out of the way, let’s get right into it.

Wattage and how much you really need


As stated above, a power supply’s wattage determines how much power it can output to your components. If you’re replacing a pre-existing power supply from a prebuilt desktop build, you’re best going with a power supply that has a higher efficiency and wattage than what you started out with, especially if you intend on upgrading things like the processor or graphics hardware. Graphics cards in particular come with their own power requirements which can usually be seen on their boxes or on the web pages you check them out from. Be sure to check this out beforehand.

As a general rule of thumb you want to learn how much electricity your components are using, and then you want to buy a power supply that has at least a hundred, preferably a couple hundred, watts above what your components will use. Using a power supply that’s “just enough” can cause it unnecessary stress and could lead to PSU failure, which can be as simple as your computer not working or your PSU actually exploding. You probably don’t want that.

In order to calculate the wattage of your components, I recommend using Newegg’s Power Supply Calculator or PC Part Picker for a good wattage requirement quote.

Efficiency – the higher you can afford, the better


In a perfect world a PSU would only draw its wattage in power. Unfortunately, this requires a high level of efficiency to perform without PSU failure which means your typical PSU will consume more power than it needs and release more excess heat as well.

There are six levels of PSU efficiency. Definitely do not buy a power supply with just the base 80 Plus Efficiency.

  • 80 Plus offers, well, 80% efficiency.
  • 80 Plus Bronze offers 82% – 85% efficiency.
  • 80 Plus Silver offers 85% to 89% efficiency.
  • 80 Plus Gold offers 87% to 92% efficiency.
  • 80 Plus Platinum offers 89% to 94% efficiency.
  • 80 Plus Titanium offers 90 to a whopping 96% efficiency.

A power supply’s efficiency translates to how much power it consumes and how much is wasted when released as heat. In short, the more efficient the power supply, the lower your electricity bill and the lower your in-case temperatures.

Modularity and what it means


Basically, a power supply’s modularity determines how many cables come hooked into it when you buy it. This may not sound like a big deal, but understand this: it is. It very, very much is. That nightmare of cables in the above image is a non-modular power supply. Take a moment to bask in it and its true terror.

Only on a very rare occasion will you be maxing out all of the ports and cables with your power supply. Even when you are, you’ll likely want to be able to perform proper cable management to prevent thermal throttling and overheating of your machine, and that is very difficult (sometimes impossible) to do with a non-modular power supply.

A fully modular power supply is another story, however. It comes with no cables connected to it by default, allowing you full control of how to manage your power supply cables and route them throughout your case. Great, right?

Well, it would be – if fully-modular power supplies weren’t super expensive in comparison to non-modular ones.

Fortunately, a middle-ground exists in the form of semi-modular power supplies. These power supplies only come with the bare necessities of cables connected – usually the motherboard power connector – with all the rest left for you to manage on your own. This is less expensive than a fully-modular power supply and shouldn’t reasonably prevent you from being able to manage your cabling.

Branding and why it’s important


The CPU may be the “brain” of your computer, but the power supply is the heart. In the inevitable dystopian cyberpunk future where you’re able to buy replacement hearts, would you buy the randy heart off the guy in a back alley, or would you purchase your heart from a reputable heart merchant?

Okay, that one got away from me. What I’m asking is would you put your expensive components at risk by buying an off-brand, no-name power supply? If you’re reading this article at all, I hope your answer is no.

Power supplies are delicate, sometimes dangerous, pieces of hardware. You need to be buying a power supply with more than enough juice to feed your components, enough efficiency to not melt your case, modularity to ensure ease of installation and good airflow, and good branding to make sure it doesn’t fail or explode.

The brands generally considered to be the best are Corsair and SeaSonic. Aside from them, Antec, XFX and Cooler Master are also notable for making good power supplies, as well as EVGA (who traditionally only deal in Nvidia graphics cards).


Ultimately, the power supply you end up settling on may not be ideal. All I ask of you is that you buy from a trustworthy brand, you buy at least slightly above your recommended wattage, and you buy a nice, semi-modular 80+ Efficiency PSU.

If you’d like to know more or think there’s anything I missed, say something below and tell me what you’re running with.

Me, I’m using a SeaSonic in my own rig.

Image Credit: sebar1, Sickest

Christopher Harper
Christopher Harper

I'm a longtime gamer, computer nerd, and general tech enthusiast.

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