As [Sam Ben-Yaakov] points out in a recent video, you don’t often see flyback converters these days. That’s because there are smarter ways to get the same effect, which is to convert between two voltages. If you work on old gear, you’ll see plenty of these, and going through the analysis is educational, even if you’ll never actually work with the circuit. That’s what the video below shows: [Sam’s] analysis of why this circuit works.
The circuit in question uses a bridge rectifier to get a high-voltage DC voltage directly from the wall. Of course, you could just use a transformer to convert the AC to a lower AC voltage first, but then you probably need a regulator afterwards to get a stable voltage.