If you look closely at the connector, each one have a different shape. So you can't connect it backward by accident.

I found this pic

https://i.sstatic.net/cL6ME.jpg

so, looks like it should be fine? maybe?

Often, 4 of the pins are removable from the power supply connector, and the remaining 20 can only go in 1 way.

I connected many times the PSU with 24pin connector to the mainboard with 20pin ATX connector. The only problem I had is that I needed cut a bit plastic in PSU 24pin connector to allow it to accept plastic end of 20pin connector on mainboard side. Another issue, which you can face, is that many ATX boards with 20pin connector have some components close to the power supply connector, which are in collision with 24pin connector.

douglar wrote on 2025-01-18, 13:44:

Often, 4 of the pins are removable from the power supply connector, and the remaining 20 can only go in 1 way.

Unfortunately this is the case for PSU from "transition" period. So these PSU were produced just for a few years and after that all PSU used single 24 pin connector

zami555 wrote on 2025-01-18, 13:50:

douglar wrote on 2025-01-18, 13:44:

Often, 4 of the pins are removable from the power supply connector, and the remaining 20 can only go in 1 way.

Unfortunately this is the case for PSU from "transition" period. So these PSU were produced just for a few years and after that all PSU used single 24 pin connector

I just went to the Seasonic page and the new psus on their site (prime tx series) all list "MB (24/20 pins) 1 connector" and in their manual it says "Connect the mainboard end of the 24/20-Pin convertible connector to the mainboard. Depending on the mainboard, you may need to either attach or detach the 4-Pin module of the 24/20-Pin connector."

I will say I just looked up Corsair psus as well and they dont look as they do that but to say "after that all PSU used single 24 pin connector" didnt seem to ring true.

This comment just stuck me odd as I have used Seasonic psus for along time and thought they always had the 4 pin detachable so I had to look at new models, saying that the last PSU I bought for my main system 2 years ago was a Super Flower and looking at that connector in my PC and their web page of new psus they list "20+4Pin - Detachable Cables One - cable (600mm)"

So I suppose its just the brand you have.

Grem Five wrote on 2025-01-18, 15:32:

I just went to the Seasonic page and the new psus on their site (prime tx series) all list "MB (24/20 pins) 1 connector" and in their manual it says "Connect the mainboard end of the 24/20-Pin convertible connector to the mainboard. Depending on the mainboard, you may need to either attach or detach the 4-Pin module of the 24/20-Pin connector."

I'm sorry, maybe it's just my memory. The Seasonic was always too expensive for me that time, therefore I haven't followed the models for that brand. I recall just mainstream low/mid range PSUs of that time.

A new SFX BeQuiet PSU I bought recently also has 20+4 pins.

zami555 wrote on 2025-01-18, 13:50:

douglar wrote on 2025-01-18, 13:44:

Often, 4 of the pins are removable from the power supply connector, and the remaining 20 can only go in 1 way.

Unfortunately this is the case for PSU from "transition" period. So these PSU were produced just for a few years and after that all PSU used single 24 pin connector

Are you able to attach the power connector to your board, leaving 4 pins hanging off to one side?

Or you can just get this

If there's room you can plug the 24pin connector into the 20pin mobo, with 4 pins overhanging. But often there's a capacitor or such nearby that prevents it. In such cases an adaptor like in the previous post will solve the problem.

That adapter looks useful,

would this be the right one?

https://www.ebay.com.au/itm/154343263946

If not, where can I get the right adapter?

yes, that looks like the correct adapter

The ATX connector be that 20 pin or 24 pin is keyed.
The pins will only go into the connector one way.
The pins which are the extra four simply leave them hanging over the edge of the connector.

The only reason you need a 24pin to 20pin connector like that is if there is simply no room for the extra 4 pins to over hang the 20 pin connector.