US polarized plug in non-polarized outlet

After searching, I still don't know what to do with a US polarized plug (for a laptop charger, for instance) if you encounter a Japanese non-polarized outlet.

I can't find an adapter for this, and if one exists, and you plug it in reversed, you'll put the hot side on the line on what should be the neutral. And there's no easy way, with a non-polarized outlet, to tell which side is hot.

you can insert to any directions. the results are same. Japanese do not care the directions. I don't know how common 3-pin plugs are in US. When I was in US, most were 2-pin plugs.
you should check the input range of your AC power adapter. if it says AC 100-240V, you have no problem in Japan.
if your AC adapter has US 3-pin plugs, you can buy an adapter(connector) which changes from 3-pin to 2-pin at 100yen shops or electric good shops in Japan.

Where have you been looking?
It is time to get a tablet that has the USB charger with the exactly the same shape/size 2 prongs even in US, which requires no adaptor in Japan.
If not, go to any hardware store, i.e. Home Depot, to get the 3 prongs to 2 adaptor for 50 cents. But I'd file off the wide tip on one blade to make it exactly the same shape/size as the other blade, if you want, to make compatible with any plugs in Japan. You may not encounter this issue at all in where you go but just in case at an older establishment.
The polarity doesn't matter as the charger converts the line AC to low voltage DC.

Thanks, Ken and amazinga. amazinga, I think your home-made adapter (with the wide prong filed down) will work if I encounter an old non-polarized outlet. BUT: as an electrical engineer, I have to ask myself WHY the engineers at Apple put a polarized plug on the laptop's power supply. They could have used an un-polarized plug, but didn't. With your modified adapter, there's a 50% chance of the hot side of the line being connected to what the power supply assumes is the neutral. That's why I can't BUY such an adapter - its sale in the US is illegal, because in some cases it could lead to a safety hazard. That's what I'm concerned about.

In fact, a bit of googling on some Apple forums shows people feeling an electrical tingling from the case of their MacBook. This seems to indicate that some sort of neutral reference is passed through the power adapter from the AC to the DC side - the DC side doesn't seem to be completely isolated.

As I said some old receptacle in Japan can not accept the fat tipped blade or you will crack it, if forced. If you don't want to file off, don't do it. It is up to you.
If you are an Electrical engineer(strange that you don't even know where to get the 3 to 2 prong adaptor in US), you can afford ASUS T100 Laptop/tablet that usees USB charger and the battery last 10hrs at the half price of MS Surface.