Japan electricity is 110 volts at 50 cycles.

This causes American made appliances to run slower, since their motors don't receive enough voltage and current.

Housing will provide you with one transformer for use during your entire tour.

Transformers will boost the voltage up by 3-5 volts and are typically used for big screen TV’s and computers. Items such as digital clocks, tape decks, and record players will run slower on the 50 cycle current, and will lose 10 minutes on the hour so will be unreliable for time telling.

Most stereo equipment sold through the Yokosuka Navy Exchange has changeover capability from 50 to 60 cycles.

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Off-base you only need Transformers for the big stuff like the TV and computers.

The American lamps, to vacuum cleaners, coffee makers etc. work just fine oh the Japanese power.

There is not a grounding prong (which is that third one on the bottom) out in town.

So make sure to use the surge protectors.

Buy the two prong Japanese ones and plug everything else into them. (except for the transformers).

It cuts the electric bill in half too because when you leave or go on a vacation, you just unplug one cord and then nothing is ghosting electricity while your not using it.
 
Some places off-base you may find that use both American power and Japanese power.  For instance: Some houses stove and washer/dryer, microwave all the big stuff has American style outlets with their own fuse box. Down side is you can't run any said appliance with the others. Like the dryer/washer with the microwave or the stove with the microwave, it pops a fuse every time. You can do the washer and dryer at the same time though. They can pull the correct current for them, but when you pull over that "poof" you will blow a fuse.
This is using all American appliances as well.

Typically you won't find to many homes that have dual power options, so just understand, that you will likely be on Japanese only power.