ATX vs SFX: The best power supply unit

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ATX and SFX are the two most common power supply units in existence. Depending on what your needs are, you can go with any of these two, but it would be wise if you could have the knowledge on what features or capabilities set them apart of each other. On this article we bring you a comparison between ATX vs SFX power supplies and what should be the criteria when buying one. The prices and power capacity vary a lot, so we will cover only those deciding main aspects, trying not to be so specific.



Currently, there are more types of power supplies that can be bought for our PC, but the most common are the ATX vs SFX. The first is the most used of all, found in many computers, especially gaming and high-end builds, but the second is designed for more compact computer formats. However, a lot has evolved regards to SFX and has quickly become a PSU of choice.

ATX vs SFX: Main differences

Starting with ATX (Advanced Technology eXtended), this format of power supply has been around since forever, first appearing in computing since matters in 1995. It was created by Intel to improve on the old AT design, which was very inefficient and extremely complicated in terms of functionality. It was introduced with 3 types of connectors: 4-pin Molex, 4-pin Floppy, 20-pin ATX and a supplemental 6-pin connector.

That said, the ATX power supply units that we see currently have evolved a lot since its inception, including new cabling such as EPS for the CPU or PCIe to feed the GPU directly. We do not want to get into the history of the ATX, since most of the improvements have to do with its internal components, rails, the capacitors, etc.

One of the most notable differences is its size: 150mm wide x 86mm high and 140mm deep. These measures allow ATX power units to provide a lot of juice (up to 2000W), including certain cooling capacities and bringing top-market electronic components.

On the other hand, we have the SFX power supply units, measuring 125 x 63.5 x 100 mm. However, don’t let their size fool you, in terms of power specifications, they are almost identical to ATXs, having the same wiring. Furthermore, it is true the size reduction comes with a price, keep reading to learn more.

Its cooling becomes quite a challenge, because the smaller the space, the more difficult it is to cool the heat generated by the electrical components. Its small form factor has moved manufacturers to use small diameter 60 mm fans to cool these units. It goes without saying for a high-performance PSU this goes far beyond its capability.

ATX vs SFX motherboard size comparison

Here is the dilemma, because of the cooling situation users prefer to use SFX in less power intensive options, and benefit from the small size of the computers with a decent cooling level. But cooling is just half of the story, also the price and durability is another factor to consider if you wish to have one of these.

Advantages and disadvantages of ATX

We will start by doing a pros and cons of each PSU format in order to be as unbiased as possible.

Pros

First of all, the market is flooded with a wide variety of ATX power supply units ranging from different power levels, wiring and energy certifications. This is something we don’t see in SFX, which of course translates to a better price because, it has enough demand to encourage manufacturers to offer more variety.

Second, we have to talk about cooling: there are active and passive sources. It is true that passive power supplies are very expensive and requires from the user a very clear understanding about the concepts of cooling to avoid overheating. You can easily fry your power supply unit or any other computer component if you don’t know what you’re doing. This improvement in cooling is due to having the standard recommended size for a power supply unit.

By using a larger fan ATX power supply units reduce significantly the noise generation, because they produce a lot more air flow with less RPMs, satisfying successfully the thermal needs.

To cap all this off, the power generation (the most important factor) is greater in ATX power units, not to mention the durability. In the event that you have a faulty ATX power supply unit, you can replace it with less effort than having an SFX.

To finish with the advantages, the power is greater than in SFX and, presumably, the durability or useful life of the source. Having more space to work and install components favors a longer useful life.

Cons

Obviously, ATX box dimensions are not compatible with smaller boxes (Mini-ITX, mainly). This form factor has become more popular recently more and more people embark on assembling PCs of this type, since it is the happy medium between a laptop and a desktop PC.

Also, with greater demand comes greater variety of ATX products. With this, we are not referring to the top or medium tier segment, rather we are talking about the poor-quality options that has swarmed the PSU market. Leaving brand names aside, they entice users with their incredible low prices, which is a critical point when looking for a power supply. If you see a computer power supply price that is too good to be true, that should be a red flag for you.

Ultimately, the noise generation is not always better on an ATX for having a bigger fan. This will depend on a greater extend in the quality of the product. It is less likely you will end up with a quiet model by having a below average or questionable power supply brand.

Advantages and disadvantages of SFX

To draw conclusions in the SFX vs ATX comparison, you also have to analyze the pros and cons of the smaller power supplies, the SFX units.

Pros

Regarding the advantages of an SFX, the first and most obvious of them all, is its compact size, which allow compatibility with many PC cases. It is true that there are Mini-ITX boxes that can support ATX as a power source, but normally ATX computer cases will support SFX power units as default because of its size.

Can we use SFX in an ATX box? Yes, you can use power supplies in ATX boxes, although it would be necessary to use an adapter. This is to avoid having the power supply unit rattling inside the computer case. There are screws that secure the PSUs to the back of the case (in most cases), so they remain fixed to the PC frame at all times.

Lastly, it might seem curious, but very rarely you will encounter problems while installing a SFX power supply on any computer case. This is something we don’t see with ATX power supplies, when sometimes you have to fiddle your way in to have them properly fixed to your computer frame.

Cons

All these disadvantages listed below might give you a sense that we didn’t take the right approach of making this comparison as unbiased and fair as possible. The truth is, as much as we wanted SFXs to be the perfect power supply solution available (who wouldn’t want to have a super tiny computer with all the power you can possibly fit in), there is a long way to go for them. Here are the cons of SFX:

  • Small variety. As the demand is less for this type of power supply units, there is not an overwhelming stock. It is really an engineering and manufacturing achievement to come up with a functional version of computer power supply almost half the size.
  • High price. This is a consequence of the above, and although the availability of these power supply units has been impacted by the 2020 and 2021’s chips shortage and United States tariff measures, the prices has been improving over time, since it is no longer a novelty. Also in terms of price / power capacity, this won’t be anything like the ATX power supply units.
  • Noise generation. Due to having a smaller fan than normal and the cooling needs that you may need in a Mini-ITX case, it is going to have a higher RPM, which causes more loudness. It depends on the model, but if you buy a good SFX source, you won’t have many issues with this.
  • Difficulty in finding a good energy certification. Linked with the price and the availability, there is the debate of a decent 80 PLUS energy efficiency, which is not an easy thing to find while looking for a SFX. We not only want the most amount of watts, but we also want to spend as little as possible in power consumption in our electrical bill. Normally, we see 80 PLUS Gold, which is not bad, but difficult to find a Titanium or Platinum.
  • Very tight cooling. As a consequence of its lack of cooling power, we must take care of it throughout the PC, since we don’t have passive SFX options (and if they exist they are a rare sight), so it is clear that it is an important issue that doesn’t leave SFX units in a very good standing.

Finally, and separately, it is worth talking about the life expectancy of these power sources because it cannot be left out the fact that this is an important disadvantage. It is normal to find the lifespan of an ATX power supply rated at 5 years of use. It can go way beyond that mark. Unlike the ATX, SFX will hardly surpass this average.

ATX vs SFX conclusions

Each PSU format does its job, with SFX targeting a more compact market and ATX targeting a tower and semi-tower market. However, there are mini-ITX boxes that accept ATX, which is a handicap for SFX sources.

if we have to give a verdict, the victory of this ATX vs SFX comparison goes to the ATX because of the following:

  • More “reasonable” prices, even though they are more expensive than ever.
  • Wide catalog.
  • More interesting cooling solutions.
  • Lower noise in good models.
  • Years of warranty / lifespan. Clarify that it is striking that manufacturers grant a long warranty to ATX and not to SFX (except high-priced models), which sets off all the alarms for the consumer.

We hope you find this comparative information useful.

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