PSU super clean and stable design

[isopropilick]

I want to design a bench psu but the first step to do it is a stable base main power supply, i want to know what i need to consider and if possible a base design of a source of 40v DC

[mariush]

Here's a schematic for a 50v 1A adjustable linear power supply... attached to the bottom of this post.

As you can see, such power supplies use custom transformers with multiple windings, and connect these windings in series using relays as needed (to keep the input DC voltage just a bit above the user configured output volage).
There's also separate winding for the opamps and for driving those relays.

Also attaching a HP power supply "operating and service manual", which contains a schematic list of parts . Hope it may help.