This project has been stalled in favour of the new 600W plug-in: GxR-ONE
https://smallformfactor.net/forum/threads/gxr-one-atx-plugin-psu-a-g-unique-and-r-evolutionary-power-solution-rtx3080-ready.14671/
This thread is meant to collect your builds and experience with DC-DC power supplies such as the commonly known plug-in picoPSU.
Thehack already started a very good Guide to 12V PSU some years ago. (thank you!)
Another very good guide for beginners was published by LAZER3D: DC-DC Power Supply...