All I asked was information. Presumably, you have, at some point, verified that the devices you use actually meet their advertised specifications.
for simplicity reducing the answer to the PowerTrends switcher:
yes and no. What I have verified is that "the device I use" in my design works better than needed. I, as opposed to Mr. Erlacher, do not care how a device works if put in another design.

and the units that take AC input have a transformer
I have neither AC input nor transformer.

I have, however, never encountered even ONE small switcher, on the order of 1 ampere output rating or less, that was (a) actually capable of what its datasheet claimed, and (b) was satisfactory for use with any serious MCU application.
Have you tried PowerTrends?, if not, here is an opportunity for you to 'experiment'.

Now, you've stated that you use the switching regulator as a pre-regulator for your primary Vcc (3V3) and that's probably a good thing, but I'm curious what YOU have found, since you use these products all the time.
whether 3V3 is even involved (i.e. when 5V is the only voltage) I still use the PT switchers.

I don't, at least so far, care about the filtering you apply. Since you use these small switchers, I figured you could shed some light on what they actually do.
light: they (PT switchers) perform wonderfully when the output is adequately filtered. I have no idea how they perform otherwise, I would never dream of even trying, to use a switcher without adequate filtering would be sheer folly. my pi filter is 100uF electrolytic parallel with 1uF ceramic at the switcher a ferrite and 100uF electrolytic parallel with 1uF ceramic after the ferrite.

BTW, I do use switchers when practical, just not small ones. Fewer and fewer applications demand the 80 to 100-ampere multi-output supply, though, and fewer and fewer of them tolerate the switching noise ...
Re switching noise: my uCs sit next to 2 50A switchers and have no poroblem.

Erik

PS I amy have more reason to use switchers than most I have no control over my 'input voltage' it IS 18-32V DC.