It seems fairly common for electronic products these days to have automatically switching current adapters. Look at the scanners that interest you, and check the specs. Then you only need a simple adapter for the plug--the ones that come with voltage converters usually work. I often travel to Europe with my laptop, and I do this all the time.
It's also not such a big deal to use a voltage converter, if you need one. They're used for things like blow dryers, which draw more current than a scanner.
Another option, easier to transport than a scanner--digital camera and a thin lightpad. Use a lateral arm on your tripod to turn it into a copy stand. Once you get the hang of adjusting the files that the camera produces (they will usually be lower in contrast than what a scanner generates), the quality is plenty for screen display.