Israel uses a different plug shape than used in America, as well as a different voltage for power outlets (if I'm not mistaken, Israel uses 220V, while USA 110V).
I could use an adapter like this one:
or a converter, like this one:
Is there a way to know which is needed? ...thus far, I've been asking friends about what they've used (phone/computer = adapter; shaver/alarm clock = converter) and so far it's worked...but I'd much rather know why different devices work differently, and if there's a way to know for certain without the need to rely on friends' (nonprofessional) opinions. (also, not blowing stuff up has its advantages...)