Riktw writes to inform us of a tutorial site covering the theory behind capacitors, and inductors, as well as noise suppression filters. The site is actually a blog, with new posts being posted every month or so.
When looking for a small switching power supply module at the website of Murata I found this Emicon-Fun! They have some lessons about how capacitors and inductors work.
Of course, as they make caps and coils it’s a bit self promotion but the lessons look quite useful.
Via the forum.