I have an ATX supply with 12v dc output leads. I have a usb-c powered device which can only consume 12v dc coming in on usb-c and needs to be signalled, or attached to a power source which matches the signals. I do not need a buck conversion. I need the supply side signalling suitable to act as a 12v usb-c output, to connect to the devices usb-c input. A pd trigger appears to be a chipset which acts as a device needing power and accepts voltage in on usb-c to put out, offering the client side signals to trigger 12v to be emitted.

I want the other direction: the chipset and logic which would be inside a 12v power source emitting usb-c.

It doesn't help that 12v was the voltage emitted from the final specification, it's optional.