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PC power-supply wire colors remain recognizable because the familiar mapping has been carried forward in ATX design guides for decades. But it is a convention, not a universal requirement: Intel’s 1998 guide explicitly called its suggested colors “NOT required.” The reviewed guides show continuity, not an official explanation for why it began or persisted.
What the common PSU wire colors mean
Intel’s displayed ATX Version 3.0 Multi Rail guide, version 2.01 dated February 1, 2023, assigns these colors to signals on the 24-pin main power connector:
| Wire color | Signal in the displayed Intel guide |
|---|---|
| Orange | +3.3 V |
| Orange with brown | +3.3 V default-sense wire on pin 13 |
| Red | +5 V |
| Yellow | +12 V |
| Black | COM |
| Green | PS_ON# |
| Gray | PWR_OK |
| Purple | +5VSB |
| Blue | -12 V |
This is a guide’s connector mapping, not proof that every PSU cable uses those colors. The cited guide page is labeled version 2.01 and says a newer version is available, so this table should not be treated as the latest revision. Intel ATX Version 3.0 Multi Rail Desktop Platform Power Supply Design Guide
Why a decades-old convention remains
The continuity is visible in Intel’s guides: familiar colors appear in both its 1998 ATX guide and its displayed 2023 guide. Reusing a recognizable scheme may make wires easier to identify and preserve familiarity across generations, but the reviewed documents do not give that as the official historical reason. It is an inference, not a documented explanation.
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- [8-in-1 ATX Power Supply Tester] -- Support test 20-pin ATX / 24-pin ATX / HDD (IDE) / Floppy 4-pin / PCI-e 6-pin / 4-pin / EPS 8-pin (NOTE: can not fit for PCI-e 8-pin) / SATA connectors
- [Aluminum Alloy Enclosure] -- Light and Easy to Carry, High Strength, Nice Thermal Conductivity & Corrosion Resistance
- [1.8'' LCD Screen] -- Outputted Voltages shows on the 1.8'' LCD Screen, Easy to Read ( The 1.8'' LCD Screen was Powered by 20-pin / 24-pin Connector ), Note: The Product Screen Has a Load of Scratches All Over It？Because The Screen is Easy to Scratch, We Put a Protective Film on It, If You Think It's Not Beautiful, You Can Tear It Off by Yourself
- [Beep Alarm] -- When your power supply test value is beyond normal range, the Power Supply Tester would issue a buzzer alarm, Easy to Know
- NOTE: The voltage of 20pin / 24pin connectors is displayed by the LCD Screen, as "+3.3V", "+12V1", "+5V", "-12V", "5VSB", "PG" (except "+12V2" on LCD Screen); The voltage of PCI-e 6P / 4P / EPS P8 connectors is displayed by the LCD Screen as "+12V2"
The important qualification is that Intel’s 1998 ATX Power Supply Design Guide, version 0.9, describes the coding as suggested and says it is “NOT required.” That makes it more accurate to call the mapping a long-lived convention repeated in design guides than a compulsory or universally enforced standard. Intel ATX Power Supply Design Guide, version 0.9 (1998)
The convention persisted, but the signals changed
Color continuity does not mean every rail from an old connector still exists. Intel’s 1998 table includes a white wire for -5 V. In the displayed ATX 3.0 connector table, pin 20 is reserved instead, and the white -5 V rail is absent. The older color scheme can therefore remain recognizable even as connector assignments evolve.
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Can you identify a specific PSU wire by color?
No. A general color chart is not enough to establish what a particular cable does, especially on a nonstandard or manufacturer-specific PSU. When identification matters, consult the exact unit’s label and its manufacturer’s pinout documentation. Do not use insulation color alone as a basis for probing, shorting, or modifying a power supply.
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Quick Recap
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- The LCD power tester is a powerful power test device. This power tester only needs to be connected to the ATX connector of the power supply to easily and intuitively know whether the output of each power supply is normal. It can detect ATX, BTX, ITX, TFX computer power supply, and can display various voltage and PG values in liquid crystal to quickly detect the performance of computer power supply.
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