Mike Slinn

Upgrading Modular PSUs

Published 2024-06-28. Last modified 2024-07-03.
Time to read: 8 minutes.

This page is part of the posts collection, categorized under Hardware.

This article discusses modular PSUs conforming to the family of standards for power supplies designed for ATX form factor motherboards, specifically, the ATX 2.x and ATX 3.x PSU specifications. These two major versions of the ATX PSU specification are collectively called the ATX12V specifications. ATX12V PSUs are the most common types of PSU today, having evolved from the original ATX PSU specification.

Some of the information in this article applies generally to all modular PSUs, in particular the summary.

ATX12V Standard

The ATX12V standard is upwards compatible. This means you can install a PSU that conforms to a more recent version of the standard in an older motherboard that only supports an older version of the standard. For more information, please see the ATX / ATX12V Power Supply Design Guide.

ATX 2.x PSUs

The current version of the ATX12V standard, v2.53, was released in December 2021. The most recent version of the standard that I could find a PDF of is ATX Specificaiton Version 2.2, published in 2004.

This is the ATX 2.2 24-pin motherboard power connector pinout:

ATX 2.2 24-Pin Connector Pinout Diagram<br>Pin numbering is clearly shown
ATX 2.2 24-Pin Connector Pinout Diagram
Pin numbering is clearly shown

The above diagram shows that pins are numbered in columns from left to right. pin 1 is at the top left, and pin 24 (the highest-numbered pin) is at the bottom right.

ATX 3.x PSUs

ATX 3.x is upwards compatible with ATX 2.x, which means that an ATX 2.x tester can determine if an ATX 3.x PSU works, except for being able to test either of the new high-power PCIe 5.0 connectors for top-tier GPUs.

ATX 3.0 introduced the 12VHPWR connector, which was problematic and was replaced by the new 12V-2×6 connector for ATX 3.1. To learn more about ATX 3.0, see What is ATX 3.0 and why you need to know before your next PC upgrade.

Anandtech has an excellent description of ATX 3.1 that explains why the 12VHPWR connector introduced by ATX 3.0 was a failure and discusses the 12V-2×6 connector introduced by ATX 3.1 to replace the ATX 3.0 12VHPWR connector.

I would not install an ATX 3.x PSU unless the computer had an NVIDIA 4090 because this PSU standard is still bleeding edge.

Modular PSUs

I recently encountered a bad batch of computer power supplies (PSUs). This article specifically discusses replacing / upgrading modular PSUs. Most of the issues raised do not arise unless the PSU is at least partially modular.

Non-modular PSUs lack one significant source of failure: only the cables provided with the PSU can be used because they are permanently attached.


Modular power supplies have removable cables; you only connect the cables that you need. This makes building computers easier and improves airflow within a computer.

If you attach a cable from a modular PSU to a modular PSU of a different model, then some or all of the electronics in your computer may be fried. The actual results depend on many variables.

Replace old PSU cables with the cables that come with the replacement PSU

You might want to get in the habit of marking each end of every cable with nail polish, and also paint a dab on a small portion of the PSU label as well. Using a unique color of nail polish for every different model of PSU that you own will make it easy to recognize the cables that came with each model of PSU that you have. Nail polish will not stick to the plastic used in some connectors, so if that is the case, place the dabs of nail polish on the wire sleeves, if present, or on the wires themselves.

Four Special Wires

Four of the wires in 24-pin ATX v2 and v3 cables have special functions. It is important to test new PSUs before you install them, to verify that the signals in these wires are functioning properly. This section describes the signals to be tested. The next section describes how to test them.

  • PS_ON (power on) on pin 16 is a signal originating from the motherboard to the power supply. This pin’s voltage is internally pulled up to +5 V inside the power supply. The PSU will attempt turn on after the voltage on this pin is pulled low by being connected to ground.
  • PWR_OK (power good) on pin 8 is an signal from the power supply that indicates that the +5VDC and +3.3VDC voltages provided by the PSU’s 24-pin connector have stabilized. The motherboard will not attempt to power up unless this signal is provided. Normally the singal remains low for a brief time (100 to 500 milliseconds) after the PS_ON signal is pulled low; however, the signal will only go high after the PSU ascertains that its +5VDC and +3.3VDC outputs are stable and within normal operating parameters.
  • +5 VSB (+5 V standby) on pin 9 supplies power even when the rest of the supply wire lines are off. This can be used to power the circuitry that controls the power-on signal.
  • +3.3 V sense on pin 13 allows the PSU to sense the voltage drop in the PSU wiring.

Use a PSU Tester

Always use a PSU tester to test a new power supply before you install it.

Most PSU testers have no battery and are completely powered by the PSU's 20-pin or 24-pin interface. If no power is provided by the 20-pin or 24-pin interface, the tester will not function.

To use the PSU tester shown above, plug the 24-pin cable between the PSU and the right-hand-side connector on the tester. Now turn on the PSU. You should observe:

  • The tester should NOT start beeping.
  • PG stands for Power Good, also known as “Power OK”. As previously mentioned, the motherboard will not attempt to power up unless this signal is provided. The LCD indicates how many milliseconds it takes to receive the Power Good signal from the PSU. If it reads 0, your PSU is non-functional.
  • The text under the +12V2 heading will flash LL when no PCI-E device is connected. Its value is only relevant when a PCI-E connector (4-pin, 6-pin or 8-pin) is used by an IDE (HDD) or a SATA drive, or a floppy disk.

Replace The Cabling When Replacing a Power Supply

When replacing a power supply with another model or brand, even if it seems almost identical, also replace the power cabling. Seemingly trivial differences between PSU models can cause the new power supply to fail if an old power supply's cabling is used, and the components it is electrically connected to might be damaged.

💥 💥

In other words, unless you are really, totally, absolutely 100% sure that the cables are in every way identical, replace them when you replace the PSU. Leaving the previous cabling in place and just swapping the power supply can fry the power supply, the motherboard, and more.


I have been purchasing PSUs for the computers that I build since the early 1980s. Some of those PSUs were made by Corsair.

Following the lead of other vendors, Corsair introduced its first fully modular PSU in 2012 for computer enthusiasts to build their own computers.

Technical support is not provided, citing ‘legal liability issues’. I call bullshit.

‘Legal liability issues’
‘Legal liability issues’

Technical information for specific products is not organized properly and contains inaccurate compatibility statements. Providing incomplete information seems to be a goal, perhaps again due to paranoia about legal liability. I attribute the inaccuracies to sloppiness.

Corsair's PSU products are described as mysterious black boxes, with stern warnings of fatal hazards if opened.

Connector Labels

Corsair has been inconsistent about how it has labeled the modular connectors over the years.

In the above photograph, we see:

  • Three connectors were clearly labeled with the PSUs that they were compatible with (“TXM/HX Series only”, “760/860AX ONLY”, “Type4”)
  • One connector had a label that only had meaning if you knew the PSU it was for (“CD08”)
  • One connector labels its purpose but does not provide any clue about the PSU that it was designed for (“PCI-E”). As we shall see, not all PCI-E cables are created equal.

Not shown are connectors without labels.

The inconsistent and unhelpful labeling continues today.

Inaccurate Compatibility Statements About Cabling Variants

The main Corsair product page for PSUs says:

The only difference between Type 3 and Type 4 cables is the pinout of the 24-pin ATX cable; all other cables (SATA, PCIe, etc) are the same.

However, that is incorrect. Corsair’s blog states that the 24-pin cables have the same pin-outs, and that the PCIe and EPS12V cables are not the same. This is also incorrect, because the 24-pin cables have different pin-outs.

The Type 4 cables have the same pin-out as Type 3 cables, but include small, solid capacitors on the +12V, +5V and +3.3V leads on the 24-pin, PCIe and EPS12V cables.

In summary, I understand all of the above to mean that, except for the 24-pin ATX cable, type 4 cables are compatible with type 3 cables, but they provide cleaner power.


Little diagnostic information is provided. "Use a paperclip," they say, and then they also mention that might not be very helpful. In general, paperclips have limited value as a diagnostic tool for debugging PSUs. Next, Corsair discusses how to use a PSU tester for an ATX 24-pin cable but does not talk about how to test the other cables.

Corsair provides a table on the same page showing pin signal levels for an ATX 2 24-pin cable but neglects to indicate how pins are numbered.

Alternative Manufacturers

A brief search yielded the following PSU manufacturers, all of whom provide product support:

EVGA SuperNOVA 1000 GT

I moved away from the bad batch of Corsair PSUs and purchased an EVGA SuperNOVA 1000 GT.

NewEgg now has a new AI-generated customer recommendation summary for their products, and those comments helped me make a purchasing decision. I recommend the NewEgg purchasing experience.


I opened the EVGA SuperNOVA 1000 GT box and found a proper printed manual, in color. The manual showed a US phone number for support (888-881-3842) and an email address, support@evga.com.

The included 'tester' was just a jumper that could perform the same function as a paperclip. It was almost completely useless. I used my tester, shown above. The test failed with PG=0.

I called the phone number on a Thursday at 4 PM ET, but was told it was closed until Monday at 9 AM PT. That was odd. I also called their other customer support phone number, (714) 528-4500, but got the same message.

I emailed EVGA’s support address, but the email bounced back with the following error.

<support@evga.com>: host d290004a.ess.barracudanetworks.com[]
  said: 550 permanent failure for one or more recipients
  (support@evga.com:blocked) (in reply to end of DATA command)

I emailed their European support address, supportEU@evga, with the same error. I then enrolled in the EVGA Member. However, I could not log in due to several bizarre errors.

What is going on? Is EVGA bankrupt?


Replace all cables attached to a PSU when upgrading it.

I forgive Corsair's bad batch of product, it happens. I do not forgive the policy of not providing technical support.

I will update this article after I receive and install the EVGA SuperNOVA 1000 GT.

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