In North America (and South America, Japan and some parts of the Caribbean) we use an ungrounded electrical plug that has two flat prongs (See Fig.1 Power Adapter examples below) or a grounded plug that has an additional third prong. In most of Europe, the Middle East, Africa, Asia and other parts of the Caribbean they use a plug with rounded prongs. If you want to be able to plug a device from another country into an outlet you’ll need an ac adapter. 

I’ll outline the other kinds of power adapters you may need. Most electrical adapters come in a both grounded and ungrounded versions but some counties only use three pronged plugs so the only travel adapter listed will be a grounded adapter. 
Australia, New Zealand, Fiji and China use a slanted two prong adapter.
Great Britain, Ireland, Africa, Hong Kong and Singapore use a three prong plug, with two flat prongs in line and one perpendicular.
Some places in Asia, the Middle East, Africa, Central America and the Caribbean use a grounded adapter.
Italy uses electrical outlet with 3 rounded in-line prongs.