You don't really learn anything until you have to teach it.
Learned how to teach many times in my life. Thought it would always be easy to put together a lesson plan for stuff I'd been doing my whole life until I started putting lesson plans together to teach the stuff I'd been doing my whole life. Never realized how little I knew about what I was about to teach until I had to teach it. So called "smart" people usually skip over a lot of stuff and assume some stuff is so obvious, it doesn't need to be stated. This is the main reason some teachers get so frustrated when students STILL DON'T UNDERSTAND what they're saying.
First, you have to answer all the questions you raise by yourself when trying to figure something out BY YOURSELF. Then, when light bulbs start spontaneously lighting above your brain, you realize there are things about it that are SO OBVIOUS to the person/people who originally put it together, they didn't think it was necessary to restate it. THIS, is what you have to explain to your students.
My first impression of this astron schematic is that the transformer has two outputs. The inside taps (lower voltage) go to a half wave rectifier, followed by a filter capacitor and then to the pass transistors. This provides the regulated output of 13.8 volts at up to 35 amps (higher current). The outside taps (a little higher voltage) also go through a half wave rectifier and filter capacitor and is then regulated by the UA723 (lower current) to the bases of the pass transistors (for higher current through them). My next step would be to start looking at the specifications of the UA723 to start figuring out all the reasons for all those other little discrete components around the UA723.
But I don't fix power supplies any more and I'll never teach anything about power supplies again.
Extra vignette, supplied to you free of charge... What I've learned about math: You don't really learn algebra until you're in calculus. And you don't really learn calculus until you learn its disjointed history, which started with geometry. I'm 60 years old and didn't figure this out until a few months ago. I think I'm now, finally, ready to start teaching calculus.