Is this the correct way to make the adapter? Will the "15A 120V AC ONLY" switch damage anything? The switch is illuminated. (glows when off)


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    – Chenmunka
    Jun 10, 2021 at 18:08
  • 2
    Note that new Specification 2.01 has deprecated the -5V rail, so you may have to use a LM7905: 1) GND 2) -12V from PSU 3) -5V to AT P9
    – Stavr00
    Jun 16, 2021 at 16:40
  • The switch won't glow. The switch needs 120V AC to glow. It will still work as a switch though.
    – user253751
    Jun 26, 2021 at 0:22
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    @Stavr00: Damn, beat me to it (more details here).
    – Vikki
    Jul 16, 2021 at 0:51

2 Answers 2


I second @Raffzahn the on switch is just low voltage low power digital switch its most likely just +5V or +3.3V and just few mA or less depending on the gates so using 15A/120V switch for it is overkill.

Its most likely meant to reusing the original AT case power switch for this.

In practice usually just a short-cutting wire put directly to connector is used instead (permanently on and use the PSU backside switch to on/off).

However beware in case your AT on/off switch contains also filtering resonator (part usually enclosed in plastic or ceramic casing with 3 4 or 6 pins) or dampening coils both would be very close to the switch, that should be bypassed as it might damage the PSU when used on its digital side.

Also check if the switch is not connected to case ground if it is disconnect it. You know case ground and digital GND are not the same !!! If you can't disconnect the grounding (some are fixed permanently with bolts) then its not safe to use it and impose a great hazard not just to PSU... (both health, fire and PC damage even damage crossing other devices through power cord or even signal cables like network sound ...).

The glowing is most likely just a glowing tube that does not work on low voltages so it should be fine...

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    @Brian Tompsett - 汤莱恩 heh you beat me by 11 seconds was just about to repair the same :) ... weird usually the site prevent to enter edit mode if it already is in it for other user... we had to hit the edit button in very small time frame
    – Spektre
    Jun 9, 2021 at 9:12
  • You can always edit your own posts, regardless of whether another user is editing. Jun 9, 2021 at 12:55
  • @TobySpeight not this time .. editor worked fine however saving the changes was not allowed for me
    – Spektre
    Jun 9, 2021 at 13:13
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    @Spektre, that's what I meant - another user editing won't block the post's owner from starting to edit. And whoever saves first wins, which can be frustrating. Jun 9, 2021 at 14:56
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    "You know case ground and digital GND are not the same !!!" What? Are you talking about AT power supplies? I've never seen an ATX power supply where case ground != "digital ground" (power ground/black wire).
    – Oskar Skog
    Jun 9, 2021 at 16:48

Yes, that wiring is correct for an adapter to connect an ATX supply to an AT motherboard.

You can use any on-off switch you like for turning the ATX supply on, usually ready-made adapters you can buy get wired to a switch that replaces or uses the original AT case mains switch for contolling the ATX supply. By itself, the switch won't damage anything, and is a better way to turn ATX supply on and off than simply hardwiring the PS_ON to GND and using the mains switch on the ATX supply to turn it on and off.

If your switch is an illuminated mains switch, it obviously won't be illuminated, as it most likely requires mains input for lighting up, and now it will be used for switching the ATX logic control input only.

You can also buy one of these adapters as they already exist and they should be identical to your drawing. The original AT mains switch is simply replaced or disconnected from mains wiring and rewired to control the low voltage PS_ON wire of the ATX supply.

  • 1
    I'd like to update my answer due to the downvote, but I'd need to know the reason for the downvote to do so. People use ATX supplies to power AT motherboards just fine with wiring given in the question or matching ready made cablesets, using the old mains switch to control the ATX PS_ON pin.
    – Justme
    Jun 9, 2021 at 9:32
  • Not sure why the dow-nvote but most likely because of the lack of any checking of the power switch which might pose a big problem ... so looks like it will work might be very bad wording as it might not and even might damage a lot more than just PSU
    – Spektre
    Jun 9, 2021 at 9:46
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    @Spektre What do you mean lack of any power switch checking? That switch is used exactly the way people have wired ATX to AT adapters for years.
    – Justme
    Jun 9, 2021 at 11:26
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    @Spektre But PC metal chassis will already be grounded, inside power supply mains earth is connected to power supply metal and to black 0V wires. AT supplies also may provide the yellow-green wire at the mains power switch where it can be connected to the screw that mounts the mains switch to chassis. Mains switch terminals will not be earthed, they are live&neutral from mains inlet and live&neutral to PSU input.
    – Justme
    Jun 9, 2021 at 14:08
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    @Spektre But that is not true, no part of the AT/ATX PSU floats, when properly connected with three-prong earthed mains plug to earthed outlet. The earth wire goes from plug into PSU. PSU metal case is earthed, PC case is earthed via PSU metal case, output black 0V also connects to PSU metal case and is earthed. Nothing floats - unless you connected the PC into 2-prong socket which has no earth, and this will cause problems and should not be done to begin with. Without earthing, then the metal case will dangerously float via mains Y caps, and so will everything else, and is dangerous.
    – Justme
    Jun 9, 2021 at 16:01

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