A UPS that's designed for use with computers, normally has a pretty clean sine wave.
If you do use an O-scope, remember to put the probe ground clip on the (round) ground of the outlet.
I've had a few students try to look at AC outlets and accidentally stick the probe ground clip on the hot side of the line.
It smokes the probe..
Be sure the scope/probe combo is rated for 120 AC-RMS Some scopes won't handle very much voltage and need a probe (w/ voltage divider) to get up to higher voltages.
120VAC has some pretty high Peak-to-Peak voltage..
Brushing up on ac circuit fundamentals
Jeepers, that modified sine wave sure looks like a square wave to me!!
