It does make me think of lots of other examples of this kind of thing happening long before China got involved (Jensen/Cinemag, OEP/Vigortronix, Carnhill/Sowter, etc, etc...). I think it's fair to say that companies try to copy each other all the time. The real test will be to see if these transformers are as good as what they claim. If they are, great! Even Jensen was acquired by Radial a while ago, and from what I understand, have changed some of their manufacturing practices. Is Jensen even "Jensen" anymore? As long as they make transformers that measure well, I'll keep buying them.
For me, the much bigger problem is the question of HOW are these Chinese prices so low? I saw a pair of similar Jensen-style 10k:10k transformers on AliExpress for $15 for a pair! I hate to think of what kinds of labor practices and/or environmental impact lies behind getting the price that low.