This is my bench power supply made out of an PSU. Any questions....? I'll be glad to help.
And here is the schematic.. (in the schematic there is a mistake, the USB should be connected to ground an +5 instead of -5)https://www.instructables.com/files/orig/F88/8JHO/FSSIQIA5/F888JHOFSSIQIA5.pdf
And here you can see a graphic schematic.https://www.instructables.com/files/orig/F2D/LMFU/FYYNECNH/F2DLMFUFYYNECNH.jpg