If you’re from the US, you really don’t have to worry about this since the voltage is similar between the two countries. Just ust about all electronics have a voltage regulator attached which will do a conversion for you. See the pictures below. It’s the little box you see attached to your computer cable or phone charger. If you see that, then you know it’s safe, and no plug/outlet adapter is required.
I’ve been going back and forth between Japan and the US for nearly 20 years and I’ve plugged in all of my Japanese devices in the US and I’ve plugged in all of my US devices in Japan. I’ve never once had any problems.
Sorry, but I don’t know much about other countries and an internet search would be much more reliable than anything I could tell you. I was a reseller in Japan and sold a lot of electronics to people overseas (Europe, Middle East, Asia) and most people will need a step-down converter and/or a special plug adapter. Do a Google search for “step down converter and plug adapter for Japan” or you can check eBay.
Finally, if you are renting a mobile internet dongle, most companies usually give you an extra battery pack. It uses a phone usb cable so you can use it on your phone if you need to. That, plus a regular charging cable, kept me charged all day. Just be prepared to bring everything around with you.
Japan uses the same batteries that are used overseas (AA, AAA, etc.) and you can pick them up at convenience stores. They also have mobile power charges you can buy on the spot if you find yourself in a bind. Taking pictures and video constantly almost always required a recharge sometime before the end of the day.
If you buy a camera and want to shop it back home, keep in mind that you cannot ship lithium ion batteries through the post office. Take it with you on your carry-on or be prepared to buy a replacement when you get home.