@Cinerion Eremita Montanus there's some good books because transformers are varied and interesting. Like, instead of paying >$50 for a balun for a vertical antenna (or a crappy offset dipole) you can just wind 10 meters of spare coax around a soda or bleach bottle (you know the size) and zip tie it in that form. it's a transformer, a balance to unbalanced transformer.

i have a PSU with the toroid in it like you have there. It is 5V DC at 10 amps or something stupid like that, and it's VPP ripple is like 2microvolts