Most modern office buildings and hotels are 3 prong now and have locking (i.e. you twist the plug to lock it in place) sockets. If you are traveling to a variety of types of offices, or not sure of the hotel's sockets, I recommend a three to two prong adapter be kept in your case as mentioned above. If you are travelling to Tokyo and its bigger complexes you will not need the adaptor. I would in any case treat it much as an umbrella being brough to prevent rain. Three to Two adaptors are widely available if you get here and ar stuck. Worst case post me a amil message and I will advise where to get the adaptor nearest where you will be.

Best,

Mike