Did you ever check the physical dimensions of the existing toggle switch?

No, but i will do once i'm home 😀 thanks for the reminder

I decided to go for ATX to AT adapter. The classic on/off switch now works as i hoped. The old PSU had a 2 pin power cable for the turbo led. I fixed this with a power-led splitter from ali.

Could you use an arcade machine square push button?

https://www.ebay.co.uk/itm/313951858564?

edit, ah, no. The hole size is 25mm, but the switch itself is 33mm. Probably too big.

geertjanb wrote on 2024-12-30, 14:40:

Unfortunately it didn't work, i removed the 2 pins from the ATX plug, connected them to the AT switch. Connected the ATX power connector to the mainboard. Switching the AT power button on turns the fans etc on, the mobo gets power, just nothing happens. No beep, no post, no nothing. It seems like it gets power but doesn't 'know' that it's turned on?

So you're going to use a AT style switch(or say, "Power Button") with ATX board and ATX power supply?
this may be doable with some help with MCU or some Arduino-style controller to monitor the state of that connected AT style switch, and a relay switch to fire a pulse to modern ATX power button (i.e. simulating pressing and releasing power button) when AT style switch state is changed.

Everything works now with a simple ATX to AT adapter 😀