How do I turn on/off the "beep" when the iPad is plugged into power?

If you've the sound turned down, or if you've got notification muted, then you won't hear it.

Depending on what you've got Settings > General > Use Side Switch To set to (mute or rotation lock), then you can mute notifications by the switch on the right hand side of the iPad, or via the taskbar : double-click the home button; slide from the left; and it's the icon far left; press home again to exit the taskbar. The function that isn't on the side switch is set via the taskbar instead : http://support.apple.com/kb/HT4085

Is the slide switch on the side set to "off?" This will cause the beep to not sound.

That works...thanks a million!

Your solution did it!🙂