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I have a laptop power brick with this symbol on it.
It reminds me of a Class II symbol:
but is, obviously, different.
The central symbol looks like a noiseless (clean) earth (ground) symbol (see here):
It's unclear what the two symbols might mean if they're nested.
1I'm afraid this does not answer the question since it does not address the meaning of the symbol I asked about, but, rather, repeats information already included in the question concerning one of the component symbols. – Richard – 2018-05-29T05:26:40.500