▷ Power supply formats: atx, sfx, sfx

Surely you've heard of the format or form factor of a power supply. This is one of the most important characteristics to take into account when buying equipment, since in case of incompatibilities you can have serious problems when assembling your equipment. Are you ready to know everything about this? Let's go there!

Index of contents

What is the format of a power supply for?

When a font has a specific format, it means that it has defined dimensions and anchor points to specific PC towers.

The existence of solid and defined formats is really positive. Imagine a market where each chassis made use of its own power supply format, being limited to using boxes with included power supply and exclusive and expensive replacements, or forced to buy own sources from the manufacturer that might not be of good quality. In short, a disaster.

On the other hand, if there were only one single format it would also be disastrous, considering that not all of us have the same needs. A source with a normal / large chassis will allow you to build models with higher power and fewer cooling problems, but it will not be much fun for someone who is going to build a small unit and need less than 600W of power.

In this article we do not mean the same thing when we talk about “format” and “standard”. By the first we mean defined dimensions and by the second defined electrical behavior standards.

Most of the sources that we are going to see here, especially those that we mark for domestic use, make use of the ATX standard. It is important to clarify the difference between the "ATX standard" and the "ATX format" as we do well above. It is a matter of economics of language and trying to make the concepts clear throughout the article.

Specifically, this standard defines what is considered adequate behavior of a power supply, that is: how it should be turned on, what voltages it should have, what protections it should include, under what harmony the rails of the source should work, etc. Interestingly, this standard is fully developed and controlled by Intel.

Having said all this, it's time to see the different formats available. Here we go!

Most used formats in the domestic environment

Here are the most important formats that the market offers:

ATX format: 'the one of a lifetime'

(We remember that we are referring to the form factor and not to the homonymous standard)

The first thing to note is that ATX is by far the most widely used format in today's power supplies. Most 'normal' size PC chassis are made to equip such a font.

It is worth mentioning that the two standard ATX formats are ATX PS / 2 and ATX PS / 3, differentiated by their depth of 140mm and 100mm, respectively. This is only relevant in pre-assembled PC sources, and not in piecemeal equipment.

The mandatory measurements are 150mm wide and 86mm high, with a depth that depends on the model. Generally, most sources up to actual 650 or 750W are between 140mm and 160mm. Very high capacity fountains are usually around 180 to 200mm, although there is an increasing war to offer the most compact depths possible.

SFX format: designed for compact equipment

We could say that, in the piece-based PC market (in pre- assemblies is another story), the second most used format is SFX, since it is the most common in ultra-compact PC assemblies, the so-called Small Form Factor (SFF).

So that you can compare in a very visual way between the different formats, we are going to use realistic 3D models of sources of different formats.

As you can see in the images, if we put it in comparison with the ATX we find some very noticeably reduced dimensions, and that is that the format has dimensions of 125 mm wide x 63.5 mm high x 100 mm in diameter, a difference important compared to the 150mm x 86mm x> 140mm of its big brother.

The tight interior of a 650W SFX source. Image: tech-review.de

Creating an SFX font involves several challenges and limitations at the engineering level. The fact of stuffing a high power in a reduced space implies that more work is needed when defining the cooling capacities and developing the interior of the source, since every millimeter matters, factors such as the fan not colliding with no components are really important, while there are ATX sources where even chassis is left over. All of this has 3 very obvious consequences:

1. The maximum power sources that can be developed with this format are only 600 to 700W, a far cry from the 2000W or more that has been achieved with the ATX. Later we will talk about the SFX-L that reach 800W-As it is a more difficult design to develop, not all manufacturers venture to make quality models. Coupled with the fact that it is a considerably smaller market than the ATX, the availability of SFX models is quite limited. Due to point (2), an SFX font will come out at a price higher than an ATX of similar capabilities.

So, we can conclude that, generally speaking and taking good quality sources as a reference, the ATX format is superior in sound, cooling capacities, price, power and probably durability compared to the SFX, given the absence of these limitations.

If we talk about power density, taking Silverstone data as an example, we can know that a normal 600W ATX source houses about 300W per liter, while in the case of an SFX of the same power it would be 756W per liter. ( This is simply a relationship between the physical volume inside the fountain and the power it can deliver)

Please note that SFX / SFX-L sources can be mounted in ATX boxes using a bracket (adapter). Some sources already include it.

SFX-L, complementary format to SFX

In addition to SFX, we have a variant called SFX-L, which is receiving quite a bit of attention today. The reason why it exists is to stop being tied to the use of 80mm or 92mm fans, in order to make use of larger diameter models with better sound and possibly greater ventilation capacity.

As we show you in the image, the only change is in the length, which increases to accommodate a fan of this diameter. Width and height are maintained. So we went from 125 x 63.5 x 100mm to 125 x 63.5 x 130mm.

The biggest question that comes up is this: Can you use an SFX-L font with an SFX box? Since the only thing that changes is the depth, the only requirement is that the box leaves enough space to install it and insert the cables. It is the same case as ATX boxes, where some may not support sources of 1000W or more with long lengths. A practical example is NCASE M1, which does allow you to use SFX-L as long as you don't install too large a graph.

It should be noted that the drawback of the system is that it is necessary to use fans of the 'slim' type, that is, with a reduced thickness. The problem is in the little variety on the market of this type of fan, and especially the shortage of models with high durability. It is a problem that does not occur in normal SFX sources, where the 80 / 92mm fans used are of normal type.

TFX format: very minority in pieces PC

The TFX is an extremely minority format in the PC PC market, with a little more presence in pre-assembled equipment.

Well, this physically very long format is another one more designed for small equipment, and especially for “slim” type boxes that are quite long and thin at the same time.

Regarding its measurements, they are 85mm wide, 65mm high and 175mm deep. In some cases, they have a height of 5mm more on the fan side, to be able to house it. That is the case of the source that we show you in our 3D model.

If we already considered the SFX format as “a bit limited”, the TFX is even more so, the power, availability and price limitations are even greater, reaching the point that in the consumer market the most powerful TFX source is as only 350W.

After taking a look at the complete list of sources with 80 Plus certificate, of 150 TFX sources that are certified, none exceeds 400W of power…

So, it is not a format used precisely for very high-performance equipment, although the aforementioned power is enough to power a PC with a graphics card such as the GTX 1060 or even 1070.

Formats used for servers (and some pre-assembled PCs)

Here we will list various formats used mainly on servers, but also on certain pre-assembled computers. These are the ones that are, by far, less common in the domestic market and that we can find less in stores.

Flex ATX

This is a format that is especially used in pre-assembled equipment, and we do not include it among the most common formats since the availability of models on the market is very limited. It is a format that is sometimes mistakenly called the 'mini-ITX format', when in fact it does not exist. Its common dimensions are 81.5mm wide, 40.5mm high and 150mm deep, although the latter may vary depending on the model.

It is worth mentioning that it is only used in very low capacity models, such as 250W and the like, and unfortunately they need to make use of 4cm diameter fans, which move little air and are highly noisy.

Rack Mount Formats: 1U, 2U…

These formats are created purely for mounting in racks, a type of box used in servers and, specifically, U refers to a unit of measurement (Rack Unit) that is equivalent to 44.50 millimeters. Generally, rack mount power supplies are typically in 1U or 2U format and are prepared for mounting in rack boxes of the same height. Typical measurements are as follows:

• 1U: 100mm width, 40.5mm height, depth varies 2U: 100mm width, 70mm height, depth that varies

As you can see, 1U shares height with the FlexATX, but the latter has a smaller width, so in no case is it the same format. It should also be noted that the measurements above are the most common, but the length can also vary depending on the source and the box. What should always be maintained is height.

In this type of equipment, redundant sources are also very common, and in the 1U format they are based on dividing it in two horizontally, and vertically / horizontally in the 2U.

Custom format

According to the data we have, this is the most used font format on servers. Rather, it is not a format that exists as such as we are talking about fully custom sizes, shapes, and mounting systems that vary from source to source.

As we show you in the image, we find a wide variety of formats that are totally incompatible with each other and company owners. Basically, we have tested 4 random sources from the 80 Plus certification website (Plug Load Solutions) and we have compared them in the same image.

Although it is a fairly common practice on servers (and also on many pre-assembled equipment, generally slight modifications to the ATX format), this would be chaotic if it were transferred to PCs by pieces, making things much more difficult when choosing a font and leaving a very restricted number of choices, as we explained before.

Already obsolete formats: the CPX

Not all formats resist the pressure of time, and we are going to tell you a bit about a rather curious one, the CPX.

In 2009, the Antec brand introduced the CPX format which is basically an ATX with a height of just over 120mm in order to allow a 120mm fan to be installed in the front or rear of the source, and not be limited to use of 80mm fans.

CPX (left) vs ATX (right). Photo: JonnyGURU.com

Today, the ventilation format that we see in the second photo is unthinkable in a high-end source, but many engineers still think that it is the best form of cooling since it allows a linear displacement of the air, minimizing turbulence. What Antec tried in 2009 was to combine the advantages of ATX sources with 120mm fans on the top and others with 80mm on the front or rear. First, with a larger diameter fan, more silence can be achieved. Second, the vertical positions stress less and make the hydrodynamic bearings used in many PC fans and supplies quieter. As a third point,

Actually, this information about the CPX format only serves as anecdote, as it is already completely obsolete. In any case, surely there are still some people using this box and font format in their homes, and have we even seen them recently in the second-hand market?

Other obsolete formats

We found the CPX a rather interesting format, but there are many more that have stopped being used in recent years. We do not know if they are still in use by some strange manufacturer, but our most recent references date from 2009.

CFX (left) and LFX (right)

Specifically, we talk about the CFX and LFX, with the shapes and sizes that you see in the images. What most betrays their obsolescence is that they were intended to be used in equipment with BTX boards, a failed format that no longer exists in current equipment.

How to check which font format is compatible with my PC

After learning about all the formats available, it is worth talking about the easy ways to determine if the format of your power supply is compatible with that of the box and vice versa. There are several possible assumptions, and we will give you the solution in each of them:

• Box and font chosen for PC by pieces. Here, the solution is extremely simple: by finding the technical sheets for each component, you should be able to see what format your font uses and which ones are compatible with your box. We make an example with the Aorus P850W font and the Phanteks Evolv Shift box.

  

  

  As you can see, they are not compatible since the font is ATX format and the box supports SFX and SFX-L, much smaller formats. Pre-assembled equipment: here, the key is the same as above. Consult technical data sheets, as compatibility should appear yes or yes somewhere. What if you totally lack information about your PC / case / PSU model? Here things get much more complicated, but it is difficult to happen since somewhere there has to be a label or something that indicates what equipment it is, and Google is full of technical sheets that should include this type of compatibility. In any case, here you may have no choice but to check the measurements yourself, compare them with those of standard formats and take a look at the anchors and compare with Internet photos to find out if they are compatible. It is also very important to be careful that there are no proprietary connectors and that they are all the usual ones.

Final words and conclusion

Understanding and knowing the different formats of the power supplies is a really important aspect, especially if you want to know all the relevant aspects of the Hardware and if you want to avoid mistakes when determining the compatibility of the components, since they can be very expensive.

Something that we must emphasize is that you should not only choose a font compatible with your equipment, but also a quality model. In the market there are several models of low quality and false specifications on which these aspects go unnoticed. If you are interested in our recommendations, in our guide to best power supplies you can find several very good quality models for all budgets.

We hope you found our guide interesting and helpful, whether you are a beginner or an advanced user looking to expand your knowledge. If you have any doubt, suggestion or constructive criticism, or if you need any clarification about any information in the article or about compatibility problems, do not hesitate to leave your comment. You also have our hardware forum available, in both cases we will gladly reply.