Most electronic products are compatible with Japanese electricity. On the product itself, or on the power supply unit it should have a rating.
Usually, it`s something like this;
Input: AC100-240V ~ 50-60Hz
The US is 110 or 120 (I forget which and a search turned up both as correct...?) ~ 60 . Japan is 100 ~ 50/60.
If what you have lists 100 to 200 something - then it`s safe to use as is in Japan. If it is 110 or 120 to something, or just that alone, then it is not and you`ll need an adapter.
I`m going to take a guess that your laptop power supply unit is going to support Japanese electricity. I have never seen one that doesn`t. The big differences come between the US/Japan and Europe... But between the US and Japan, I have yet to encounter anything worthwhile that doesn`t support the other`s electricity. (After a bunch of digging around, I found only ONE item that was Japan only in my room. A cheapy little decorative light...)
If the PSU says that it works with 100V 50/60Hz - then all you need is one of those sold-anywhere 3 prong to 2 prong adapters. If that even. About half the outlets in my house are 3 pronged.
If you do need a 3 to 2, they`re available pretty much everywhere in Japan too.
Checking all the power requirements on your stuff can save a huge amount of money on adapters. The ones made to actually manage the electricity are very expensive... A waste if your stuff is already made to support it, and all you need is a $1.99 plug adapter.
