"
There is a simple though unwritten rule about power supply testing:

"Never connect the ground (common, chassis etc.) of any test equipment
to the switching node (power transistor collector, drain or power IC
output pin and its associated signals) of a switching power supply!" "

Well now that you wrote it, it is no longer unwritten. :-)

But I know what you mean. It is pretty much RF and if the caps don't short it out it can burn you some. If the voltage is high enough you don't even have to touch it. I got burned by the cathode of a damper tube in a color TV set once. That is half of about a 70 KHz sine wave clocked at 15.734 KHz. Arced to my finger, burnt and cauterized all the way to the bone. On blood, but it sure did smart. And then it felt funny for like six months after.

Can you imagine that on the chassis and probes of your scope ?