I have attached the document I was thinking of. It was written several years ago as an introduction to power supply design for mid-level engineering students and focuses on a theoretical (but very easy) understanding of the underlying processes. It does not go deeply into all of Johnson's points but rather focuses on useful approximations and estimations to produce simple, everyday supplies in a straightforward way. There is some math in there, but it is ameliorated by some examples, and in the end, the equations are very simple. The paper is written in a very conversational style - who knows, might even be fun to read.
