PS: We should keep in mind that it's very important how the gear is
designed, what components are used. Some legal mains jacks don't provide
grounding.
https://en.wikipedia.org/wiki/File:Euro-Flachstecker_2.jpg
Gear signed with this logo
https://en.wikipedia.org/wiki/File:Double_insulation_symbol.svg
usually is not connected to ground. Attention, _at least it's not
allowed to connect ground to the case of a class II device_!
Metal case, build in power supply, Europlug
http://www2.yamaha.co.jp/manual/pdf/pa/english/mixers/RM602E.pdf