So unfortunately I don't have any first-hand experience although I do have anecdotal experience in the matter.
So I enjoy hi-fi and anb I'm into listening to music more than the gear, however I have a friend who I met through work who is more of a gear focused enthusiast.
Anyway a couple of years ago he went and even though he has a very expensive main system he decided he wanted to get a nice acuphase integrated for a second small bedroom type system.
He did exactly what you said, he ordered it from Japan I think eBay or similar, and saved a ton of money and the thing looked brand new. However he ended up getting a step down transformer and unfortunately it did also as you say, it made a lot of noise.
Now he got one of the big ones but in spite of that when there was no music playing you could hear this noise in the background coming through the speakers and we pretty much universally agreed that it had to do with that transformer.
After much investigation and fooling around with it and even getting a more expensive transformer he still couldn't make it work without having added noise. Personally I think amplifiers draw too much current and their draw is not constant it's a fluctuating pull from the power and I just don't think they work very well in this way.
I would argue if you were to get much more simple item like a CD player or turntable or DAC perhaps that And have such constant fluctuation in its power draw it would probably be all right, and I have heard other people buying vintage turntables from Japan and having great success with using these stepped-out transformers.
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