any options for powering small stuff like mosfets and led's and microcontrollers for a little while on a breadboard? usb powerbank and some sort of buck/boost converter possible?
I got one of these ~3 years ago:
https://www.aliexpress.com/item/1005005145280146.html and coupled it with an old school transformer+bridge+caps AC/DC PSU (I thought I needed this kind of galvanic isolation at the time).
It works fine.
I charged batteries with it many times, because nobody told me it was a bad idea. Just as expected, no issues whatsoever (though it does consume a little bit of current, like few mA, when it's off and you apply voltage to its terminals).
Voltage regulation is off by ~10 mV. Current regulation struggles to work correctly up to about 25-35 mA, but it glitches on the safe side: sometimes it goes into CC mode and lowers voltage when it's not yet necessary. Higher than that, it works well.
One caveat in this configuration: because of the capacitive coupling between the transformer's windings, there is considerable AC voltage between either of the terminals and mains earth or a human. Of course they are in phase, so it's proper DC between the two of them, and it's a very high impedance source, but I did kill a few MOSFETs with this voltage (connect source to one of the PSU terminals, touch gate, bingo). It would make sense to add a PE connection to optionally tie one of the terminals (negative) to mains earth to avoid these issues.
The only scenario so far when I needed anything else has been when more than one power rail was required. In these cases a proper multi-channel (2 or better 3) lab PSU would be much more convenient.

Noise at 15V output with a 1.2k resistor as load, 5us/div horizontal, 10mV/div vertical:
