How do I find out whether my switched-mode power supply is galvanically separated from mains?
With a multimeter.  Measure the resistance between various "output" pins and the "input" pins.

A very high resistance (>1 meg ohm) or an open circuit means that it is isolated.  A resistance of less than 10K ohms indicates that it is not isolated.  A resistance in between those two values means that something is weird.