It does have a big old inductor though (right? Sometimes even more than one), so while it may not have transformers, it does have magnetic components that does the same thing: Store energy as magnetic flux, release it at a lower potential.
Anyway, I would start at the Wikipedia article for buck converters as it is a pretty basic but useful description of how these work even if you skip all the serious-looking math.
Yes, thatâs correct, buck converters use inductors as energy storage.
Just to be clear, you can have HF transformers that look like inductors as well, some of them are actually inductors as well.
But usually a buck converter is the most efficient because of lots of confounding reasons - in short if you limit your input voltage, your selection of FETs gives you lower losses and you also have lower copper losses and lower core losses (because you need less storage). If you are willing to go to GAN or SiC devices, then it changes again in favour of HV, but I have not seen any mainstream commercial devices going that route.
I donât know if big is what it used to beâŚ
Definitely not laminate core xfr!
I tend to look at inductors, in this application, a bit like youâd look at an auto-transformer, in the specific sense that the input and output winding is the same winding. A real transformer, the isolating kind, of course has a separate winding for the input and output. Inherently, both kinds flush magnetic energy through some kind of core, so that it can spill out again in some other place as electrical energy again.
Very very simplified, I know, but kinda works for me. Basically⌠transformers are also inductors. Inductors kinda also are transformers. The whole âtransformerlessâ notion is marketing 
Just to make things more complicated. If you have more than a ~5:1 voltage ratio in a DC-DC converter, then you will often find that the coil is tapped, and is indeed used as an auto-transformer.
Good transformers are very poor inductors. (inductance in this case adds to losses)
But then it cannot be a buck anymore?
Yup. It is then a âtapped transformer buckâ 
.
But 'tapped transformer buck is rarely used - it only wins in the ~5:1 - ~10:1 ratio - after that more exotic split-winding architectures become more efficient.
I have not worked on non isolated SMPs. They seem to be used in high power applications.
The smaller âpower adaptersâ are all isolated (which given their application is understandable).
I am fascinated by this MPPT with its DC technology (No diodes!)
The input is fed into a H bridge which reverses the polarity on the two inductors that are connected in series. The common connection is the positive which is also common with the positive input. (positive earth!)