Electronics in Japan – Do I need a travel adapter?

I think I've researched the heck out of my question but I want to make sure I'm correct.

I'm from the USA where all of my electronics have either a two prong plug or two prongs with a ground plug.

I don't necessarily need an adapter for two prong devices am I correct since Japanese outlets are two prong compatible. I would only need an travel adapter for 3 prong devices.