Hi,
Talking of adaptors that reverse the polarity, I've got a "Loblite" one that takes two 5amp plugs & a 15amp one. The 15amp socket is sideways on and the polarity is reversed. The two 5amp sockets are not.
In France, it's very common to have a two gang socket that reverses the polarity, or not, depending which socket you use.
Cheers, Pete