My wife plugged an extension cord with two items (a lamp and an alarm clock)
into an available slot on a surge protector, which is then plugged into an
outlet. The surge protector already had three other items plugged into it.

As a result, the upper socket on that outlet and an adjacent outlet have no
power, but the lower socket has power. Turning the breaker off and on did
not help. The other outlets in the room are fine.

Is this a simple case of going to the hardware store and buying two
replacement outlets, or could it be something else? Why would the lower
socket on an outlet work but not the upper?