Add a charging sound to your MacBook – CNET
If you have come to enjoy the satisfying chime your iPhone emits when you plug it in to charge it, then you might want, for the sake of consistency or convenience, to hear the same chime when you plug in your MacBook Air or MacBook Pro. (The new 12-inch MacBook features such a sound effect out of the box.)
First, open Terminal via Spotlight or by going to Applications > Utilities.
Next, copy and paste this command into Terminal and hit Enter:
defaults write com.apple.PowerChime ChimeOnAllHardware -bool true; open /System/Library/CoreServices/PowerChime.app &
Now, disconnect your MacBook from the power cord and then reconnect it and you will hear the familiar chime.
If you grow tired of hearing the chime, you can undo this change by entering this command into Terminal and pressing Enter:
defaults write com.apple.PowerChime ChimeOnAllHardware -bool false;killall PowerChime