Switchers

These things are everywhere. Sometimes called the unfortunate name of wall warts, but better called a DC Power Brick, or AC/DC adapter.

Basic Operation

A good (practical) introduction is in Learn Electronics Repair 16, LED Disco Lights. https://www.youtube.com/watch?v=XgPZ1XpVppE But of course, you can refer to Art of Electronics or Practical Electronics for Beginners. Of course, the problem is that the latter two will tell you the schematic view of operation, whereas LER will show you it on an actual circuit board...

Calculators

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  TI's LM63460

Some manufacturers will have calculators in addition to the app notes that you can use. These are often based on excel/spreadsheet software. Reference: https://www.eevblog.com/forum/projects/buck-loop-stability-tuning/msg5453216/?topicseen#msg5453216 As with any spreadsheet per B. Pease (For reference, see his columns https://archive.org/details/Bob_Pease_Lab_Notes), you can only trust it if, and only if, it doesn't have any mistakes in the formulas it's built with...

Tips/Techniques

Stock 5V and 12V

These are the most common voltages. Always try to standardize on the most common barrel plug (which is I think 2.5mm, and 5.5mm or thereabouts).

Diodes Gone Wild

He has a number of videos that diagnose broken switching power supplies and is reasonably knowledgeable about them.

Example of 5V 8-pin DIP Regulator

https://www.eevblog.com/forum/repair/need-help-to-identify-a-blown-chip-in-skynet-for-z12c-switching-power-supply/msg5445107/ It's always easy to spot the capacitor and diode.