Leakage current through "cheap" mains adapters is a problem, the voltage they float at depends on physically where-abouts in the transformer the leakage is occurring - which in reality is a lot of small leaks distributed around the layers of windings.
This is why medical grade battery eliminators are essential in medical equipment.
The allowable leakage current for domestic appliances is very high as it only expects an accidental, momentary touch from a conscious person who can pull their hand away. See BS 3456 for details.
Is it a danger - no as it is the current that is the actual problem and they current path is usually quite high impedance so it might make you jump but not do you any harm. Even so it is not pleasant but still legal.
Robert
