What are the long red and black probe leads for -- connecting the load resistor? Does it make a difference if you use a very short connection instead (or remove those leads if they are for some other purpose)?
Correct, the red and black leads connect the resistor ...
Does it make a difference if you disconnect the whole adapter & probe arrangement from the power supply? (I.e. does the noise actually come from the power supply?)
Image with whole adapter disconnected (note the V/div change)
If I switch on the PWM led light on the desk
So the noise is coming from the environmet; I am aware the noise is not coming from the PSU.
I already tried to find the source of the noise without luck and cannot "investigate" further about the environment.
I can calculate the PSU noise/ripple using the cursors whit PSU channel on and off ...
The question is: are you aware of some settings or probing technique that can help here?
I already tried Trigger Noise Reject.
The goal? Have the scope calculate correctly Pk_Pk and RMS
Thank you