We’ve open sourced our designs for a modern C64 that won’t kill your C64 it if breaks.
Using the 4A part will make it powerful enough to power a C128. Everything, well almost, you need is described in the project of github.
You can find a link to the project in our DIY Open Source Stuff page, found in the menu Misc -> Own Production.
It is rumored that the pcb can be fit inside the C64c model of the brick psu.