What I’m talking about is, for example, a keurig coffee machine having two differently shaped prongs where one prong is bigger and wider than the other, so you have to insert the wider prong into the wider port.
However, something like a phone adapter doesn’t have this, and the two prongs are the same size and shape.
Why is this?
In: 125
As others have said, the two slots in the outlet are a “hot” and a “neutral”. If you stuck a fork in the hot side, you’d zap yourself because you’ve completed a circuit with the floor (“ground”). However the neutral side is effectively connected to the floor so you’d be fine (please don’t stick a knife into either side of the socket!).
Your device has a plug that runs from the hot blade, through its circuits, and to the neutral blade. If you were to touch some part of the circuit, such as the inside of a lamp socket, you could zap yourself.
Since your device already has a switch, we want to put that on the hot wire, before the circuit. So we differentiate the prongs to force the plug to sit the right way around. Now touching the circuit when the switch is off is harmless. Some older devices didn’t have this and you could zap yourself on the chassis if you plugged it in the opposite way.
Your phone charger and similar devices convert the outlet power to a lower voltage before it goes anywhere, so it’s not (as) dangerous if you accidentally touch it. It’s not necessary to differentiate the prongs because it doesn’t matter which way it gets plugged in.
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