I don't know my terminology very well. I just bought this eGPU enclosure. It also comes with an m.2 slot I suspect that's probably what this 4 pin power slot is for.
I have a spare ATX PSU to power this thing with and it's not modular, the cables come out of the PSU box in a big messy bundle and there's no where to detach or attach cables. There's lots of different connectors that come out of this bundle but alas no square arrangement of 2 rows of 2 pins as needed by this chassis.
There are however 2 such connectors that are kind of joined together through a little plastic catch, but in a manner where you can slide them apart. It's clearly intended that you can be able to separate these if you want to, but them being attached to each other in the first place has me a little worried.
The cable from which they each branch has TKG written on it and each of the connectors has L and R printed on it respectively. If I separate them, I can definitely fit one in to the slot, but is there any reason one shouldn't do this?
UPDATE: It works!! Initially the chassis wouldn't power on but I discovered that if I simply don't plug in the 4 pin slot at all then it does. I'm pretty sure that slot is for powering an m.2 drive if you have one and that was one of the things that made me decide to buy this particular chassis so it doesn't look great but I'm hoping that if I actually had an m.2 drive to test it with, that plugging in that PSU connector to the 4 pin slot would work, but at the moment, when there is no such drive connected, the entire chassis doesn't power on. Even better still, the blackmagic card works!! This is great because the manufacturer actually responded to my email asking if it would work too late and I had already ordered it and they said it wouldn't work so the fact that it does is a big relief. Word of advice for anyone testing this with standard computer monitors instead of proper reference monitors like me, it might say "out of range" or similar on your monitor for a lot of standard video frame rates, but for testing purposes, I was able to get it to work at 60p. No good for a real project, but hopefully with a real reference monitor that wouldn't be an issue.
Sounds like what you're looking for is an ATX12V plug. It's a 2x2 connector that normally has two yellow and two black wires. It normally goes into the 2x2 receptacle on the motherboard to power the processor. In this case, the eGPU enclosure needs it for some reason, maybe for more power.
The good news is that the 2x4 breakaway connector (called EPS12V I believe) that splits into two 2x2 connectors is probably compatible with this receptacle. One of the two 2x2 pieces of the connector should fit into the eGPU's power receptacle, and the other won't. If it fits, it is probably the right connector. If two of the wires going to that connector are yellow, and two are black, then it's almost certainly the right connector.
You may have multiple of these 2x4 breakaway connectors. If so, they should behave identically, and you can break up any of them and try to fit the pieces into the ATX12V receptacle.
List of ATX power supply connectors: https://en.wikipedia.org/wiki/Power_supply_unit_(computer)#Connectors (without images, unfortunately.)
Don't forget about the big 20-pin or 24-pin main ATX motherboard power connector. Your second power supply, since it is non-modular, will need something to simulate the motherboard's power button. That's can be as simple as a switch between the PS-ON wire (green) and any ground wire (black). But hopefully your eGPU has a place to plug in the ATX motherboard power connector, and handles that on-off switching for you.
oh bugger. The results were underwhelming to the say the least. NOTHING happens. I was expecting I might have trouble getting things working right away but I must say I wasn't expecting literally nothing to happen.
I have the card in the PCIe slot on the chassis, the ATX PSU screwed in place and the cables from the PSU plugged in to the chassis 24 pin and 4 pin slots. I turned on the chassis' own switch, the PSU's switch and also plugged the thunderbolt cable in and nothing. No fans whirring, no smell of anything frying, no sound indicating I'd just broken 3 expensive pieces of equipment at once, just nothing. Any ideas? The chassis in question is this thing https://peladn.com/products/graphics-card-docking-station-1 and the PCIe card is this thing https://www.blackmagicdesign.com/au/products/decklink/techspecs/W-DLK-32 .
It's all hooked up like this https://imgur.com/a/nothing-happens-PftKNUk
Thanks so much, this is very encouraging. The eGPU chassis has it's own little built in power switch. It also has a 24 pin socket that it needs to power itself so hopefully I don't need to do anything complicated like simulating anything as I'm a little lost by that idea. The power supply itself has a power on/off switch as well.
In the interests of brevity I may have given the wrong idea of the setup. I'm trying to make use of an old Blackmagic Decklink mini-monitor 4k pcie device. I now use a laptop with TB4 ports, rather than the PC this card used to sit it. This card is actually not a GPU, which this eGPU enclosure is supposed to be for, but I'm hoping it will work just the same. It's a TB4 eGPU chassis that takes an ATX power supply and has a single PCIe 16x slot. The card is actually a 4x slot but I think it should work. Anyway there's only the one power supply, this old 600w PSU that I've cannibalised from my old PC.
Thanks for all the help mate, got it working, see update.