In diesem allgemeinverständlichen Zusammenhang:
Erdungskontakt

do you mean EARTH?

also the warning would be a whole lot clearer if it said THIS IS NOT A TRANSFORMER.
three pin plugs have live and neutral - brown and blue wires - the 3rd pin, earth, - somewhat offeset, like in UK appliances would be connected to the green and yellow wire. it is perfectly possible to plug a continental twopin plug into a threepin socket by simply ignoring the earth provision on top.

i don't think i am being very helpful here... personally i find when travelling all problems plugging into strange systems is a kind of reminder that the voltage may be different...

Die gängige Bezeichnung für einen entsprechenden Stecker ist ja Schukostecker. Erdungskontakt ist IMHO genauso gut.

@ kirsten: ground (AE) = earth (BE) ;-)