Results measuring ripple in power supplies

With my fresh new Dso (Sys 1.62, fw2.72, latest Wildat33 and gabonator 8M firmware versions), I tried to measure Ripple of an old lab-grade power supply (not switched I thought) and a PC power supply (switched)

I got a comprehensive curve from the last (on 12V DC, AC coupling), 10mv Rms which is in the specs. Frequency I can’t explaim.

But I got a lot of noise from the lab PS and a very sensitive signal to fingers touching something (print screen was taken with a wood piece to press buttons).

I compared these results with a true Rms meter, which confirmed 10mv Rms on the switched PS, but gave 2mv on the old conventional lab PS, whis sounds realistic to me.

Could someone explaim how to avoid all this noise probably external, and make a good measure ?
If this is possible with a device which cost me only 89€ in a shop from amazon France…


Nb : Wildcat 8M version allowed me to save multiple print screen without corrupting the Fat (great job bob, wildcat)