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  • I know (current) ATX PSU will turn off its power after the PC shutdown. This is good.
  • I know (old) AT PSU will leave its connectors with power on even after the PC shutdown.

Ref: https://en.wikipedia.org/wiki/Molex_connector#Motherboard

  • I also know that to bridge the Green and Black wires will start up a PSU.

Ref: https://makezine.com/projects/computer-power-supply-to-bench-power-supply-adapter/

But i want none of above. I wish to get a modern ATX PSU (which means power will be off after PC shutdown), only with one / some molex connectors always-on (power stays on after the PC shutdown).

  1. I would prefer buying a good PSU with this feature.
  2. If PSU with such feature does not exist, i would consider altering current PSU to my requirement. Please give me some directions to proceed. (Alter PSU? Alter motherboard? etc.)
  3. Using two PSU can achieve this. But this is not preferred.

Not important: Why i want this feature?

It is because I want to keep my liquid cooling loop, as well as some LED lights, on as a showcase, even after my PC shutdown.

  • As more of a software end solution to your problem: Have you tried enabling USB standby power in your BIOS and/or Operating System? This could help keep peripherals on. – Bennett Yeo Sep 19 '18 at 13:44
  • @BennettYeo - Is there a way to draw enough power from the USB headers for the water cooling loop and some LEDs? – midnite Sep 19 '18 at 14:34
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    I think that depends on the headers. In general for LEDs, I'd be surprised if they wouldn't run, but if we're including the water cooling loop that depends on the power draw for your pumping system(s). I don't think water coolers and fan coolers for that matter are designed to run when the computer is in standby/shutdown so you'd need some method of bypass. – Bennett Yeo Sep 19 '18 at 16:04
  • ekwb.com/shop/ek-xtop-ddc-3-2-pwm-elite-plexi-incl-pump This is my pump going to install. It takes 12V from molex. Always-on USB headers will not have enough voltage. – midnite Sep 19 '18 at 18:05
  • Considering standby power draw requirements as outlined in EU law there might be no such devices. Even if you are in the US I'd be surprised if US PSUs were any different since modern switching supplies as used in PCs don't really care for 110V vs 230V. – Jan Dorniak Oct 25 '18 at 2:00
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Listen, do not fool yourself. Altering the PSU will only add trouble. Why do you need this? Do you just have fun or get what you want?

Use WX-DC2412 12V 8A (https://www.alibaba.com/product-detail/12V-8A-Switching-Power-Supply-Board_60835798044.html?spm=a2700.7724838.2017115.24.42c26dd6lIniLa) or WX-DC2405 12V 4A (https://www.amazon.com/s?k=WX-DC2405&ref=nb_sb_noss)

Use this power supply only to power the pump and LED.

I also used to get my left ear with my right hand. Now the Chinese are producing many cheap, simple and reliable modules for a variety of purposes. But if you are interested, you want to understand, you have a hobby - electronics, you want to explore, test and solder for about 3 months - then I wish you good luck

P.S. I myself used the WX-DC2412 - a wonderful module. 8A is good - it is with a margin. This means that at your currents the module radiators will be barely warm.

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Have you considered using a small dedicated 12V supply to power the pump and lights? I'm not sure what the behavior of your pump is when there's no PWM signal on the fan header while the computer is powered off. It may go full power turbo on you or go off entirely. That would be for you to experiment with. I see, that the pump goes to 24 watt, depending on your LED setup you might get away with using something like a 50W 12Vdc regulated supply. Those are not too hard to find. The important thing is then to connect ground but create a separate 12V rail just for the pump and lights and not let that reverse feed your main PSU. Things might get smokey otherwise. Just take an extra connector, cut the 12V wire and feed it from the new supply; connect ground(0V) to your PSU ground(0V) so the PWM and fan speed signals won't get confused. Probably also important to use an ungrounded plug for the small supply since I bet the main PSU is already grounded(earth ground). Otherwise if you connect two earth grounded supplies, there is a decent possibility of sparks. Of course be very careful when modifying several hundred watt power supply wiring and test everything on the bench before plugging in your devices and components.

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