Yes, nice simple video and nice easy to follow explanation.
With the blue Siglent you are seeing the effect of the power supply in the scope making itself felt. If you take the blue scope and power it up, connect the probe then either put only the tip of the probe on a grounded point, or connect the probe ground to the input tip only of another mains referenced scope you will see a mains frequency ripple on the screen of both scopes. This is from the power supply of the blue Siglent which is using a capacitor across the isolation boundary to reduce HF noise from the supply. Only solutions are to ground the secondary side to mains earth ( which defeats the point of having a scope with isolated inputs), power it off internal batteries when in use and only power it to charge, or use a better power supply.
A better supply would have a grounded interwinding shield, and an isolated secondary with no capacitor to ground. It would have to be a grounded unit, and would have to have a minimum of 3kV isolation to mains earth on the secondary side ( to be the same as the scope itself) and the power cord and connector to the scope will have to be rated to that as well, and will have to pass the IEC finger test as well for isolation and touch distance. Otherwise a grounded power supply and a small DC-DC converter in the scope itself to provide the isolation needed.
