As far as I understand the isolation is achieved by a transformer(and besides this sometimes also using an optoisolator for the feedback part) in a DC-DC converter. And this is a galvanic isolation.(I don't know what really "truly isolated" means btw.)
But the transformers have leakage capacitances which means a trandformer will block unwanted DC but it will partially attenuate the AC interference. I guess the higher the ferq. the higher it will pass the unwanted interference.
I have two things where I'm totally blank about this topic. Here is an example of an isolated buck converter. Take for example the model TEN 5-2411.
What type of isolation will such a buck converter achieve? Will it help to attenuate common mode interference or differential mode interference between input and the output? And how can one infer from the datasheet the frequency range and for such isolation.
For example lets say we have this buck converter where we want to step down 24V to 5V DC. And imagine at the input these is 1MegHz 1Vpkpk common-mode noise or differential mode noise. How can we estimate the amount of the noise would appear at the 5V DC output?
Will the transformer block CM noise but not DM noise? If so, how can it help preventing ground loops? A ground loop is not CM.