Hello and a question

Hello SFF forums! Really happy to be here and hoping to get started on a new build soon. I was looking to do a build similar to ejectbutton's Gamecube Build, but I was a bit confused on how DC/ATX converters worked. I assume that the external power brick is plugged directly into the converter, but how is the DC power connected back to the Motherboard? Are there cables that can convert ATX pins back to a DC plug?