Seriously, devices that run on DC via AC/DC conversion DO NOT have polarized plugs. There is no point to have it since it's just rectifying and stepping down the AC power. This includes 99.99% of what a tourist or business traveler uses, i.e. mobile phones, notebook computers, etc.
Even the Mac Airbook (or whatever it's called) has (had?) a grounded plug but it's not polarized. Then the problem is that if you buy a cheapo Home Depot converter plug then its prongs are polarized! Then you are better off with one of those multi-converter bricks. Or actually a Euro-US type converter plug usually accepts US input and the ground part will slide above if it's slim enough.
Furthermore, if an outlet is not polarized in a JP socket then I wouldn't want to spend the night in such a place. The earthquake and fire risk is probably significant.