The green and black wires with spade connectors are for hooking up to an AT style switch.

That being said, the adapters I have purchased in the past came with a replacement power switch.

You will also want to see if any of your cards you plan on using need a -5v supply. If so, you will either need a power supply with -5v or an adapter that adds -5v.

Agree ! Yes some of the better adapters work OK but there is no real good ATX+adapter replacement for a true AT PSU on an XT, 286 or older 386 IMHO.

RetroGamer02 wrote on 2020-05-28, 23:08:

I found out you could get an adapter for converting a ATX to a AT but ran into an issue.
8><CUT
Does not convert this part of the old power supply I was hoping to replace.

What you need is, I think?, a 'momentary' switch aka 'push to make' switch.
They were for reasonable prices available on Ebay some time ago but 'they do' up to and over $10 at the moment.

There is now only a reasonably priced offer for [10 pieces]:
https://www.ebay.com/itm/Power-Switch-Push-Bu … cs/253323677440

Alternatively you can try to modify the switch that you have - read SirNickity's post in this thread:
AT style reset switch

PARKE wrote on 2020-05-29, 15:39:

What you need is, I think?, a 'momentary' switch aka 'push to make' switch. They were for reasonable prices available on Ebay so […]
Show full quote

RetroGamer02 wrote on 2020-05-28, 23:08:

I found out you could get an adapter for converting a ATX to a AT but ran into an issue.
8><CUT
Does not convert this part of the old power supply I was hoping to replace.

What you need is, I think?, a 'momentary' switch aka 'push to make' switch.
They were for reasonable prices available on Ebay some time ago but 'they do' up to and over $10 at the moment.

There is now only a reasonably priced offer for [10 pieces]:
https://www.ebay.com/itm/Power-Switch-Push-Bu … cs/253323677440

Alternatively you can try to modify the switch that you have - read SirNickity's post in this thread:
AT style reset switch

A momentary switch will not work with an ATX to AT PSU adapter. The green and black on that adapter have to be shorted together to keep the ATX PSU on when not hooked up to an ATX motherboard.

Correct, because it's the ATX mainboard that would normally "parse" the input of the momentary switch and would keep the green wire connected to ground. That's why it can turn off the system when shutting down the OS or add a 4-second delay when holding the power button.

The PSU only knows "on" or "off", depending on if the green wire is grounded or not.

Ok, yes, of course. So what does he need ?

An AT power switch, or any other toggle switch. He can just use the one from the old PSU. When removing the black shrink tubing, the terminals for connecting the two wires from the adapter should be accessible.

Another solution would be to permanently connect the two wires and use the power switch on the back of the ATX PSU, provided it has one.

I ordered this https://www.ebay.com/itm/123735050753
Gonna see if I can change title to say solved.
Thank you everyone!

You could just get a brand new AT PSU:
https://www.ebay.com/itm/Replacement-Power-Su … 872.m2749.l2649

Will keep the replacement in mind if the power supply in there does not supply -5V.
Also a pic for any wondering what I have so far its a work in progress.

get that barrel battery out of there bro

Time stamp on the pic adds to it... 😀