***Link Removed***inexpensive VFD
Not at all sure what device you might be talking about. Can you be more specific? No idea what this means?
Mexico is supposed to have the same 120 VAC 60 cycle electricity as found in USA and Canada. For the most part they provide 127 VAC 60 cycle. The problem is fluctuations and how to keep them from doing damage to your equipment. You could use Uninterruptible Power Supplies (UPS) with Automatic Voltage Regulation (AVR) but you would have to have a different UPS for a number of different appliances - computers - TV/stereo - refrigerator - etc. And there may not be any UPS large enough for things like air conditioners - which is one of the critical components due to compressor motor needs. And a UPS probably costs more than the device we have mentioned here.
General consensus of opinion is many electric problems RVers experience in Mexico is probably due to poor or inadequate wiring in many RV parks. We try to adjust to the fluctuations as best we can by using various devices intended for this purpose. These devices may also be necessary in the US and Canada but perhaps not as often. There is no way to know for sure when protection might be needed so we just use these things all the time.