I am thinking about buying receiver from US, but then I noticed that they are not like any other devices made for both voltages, but usually only for 110V. I am planing to buy Rotel or Marantz, I contacted a technician from Rotel and he told me that "The internal power transformers, both the main transformer and the standby transformer, need to be rewired to operate off of the appropriate internal winding taps". Anyone has any experience with this?
Sure, you send the unit to a Rotel service center and they will rewire the transformer - usually for a cost to you.
However, why would you buy a unit not designed for your voltage? The purpose of the non-switchable transformer is one of the black market, trying to minimize the incursion of cheap product into a semi-protected area.
You might also inquire about Rotel's warranty service when a unit is purchased in one part of the world and used in another. Most manufacturuers make it difficult to obtain warranty service on such product. Then ask yourself whether buying the unit in the US for use outside of the US is really worth the trouble.