This was especially common in rooms without ceiling lights, where a lamp plugged into the outlet served as the main light source. Flipping the switch would then turn that lamp on or off.
Sometimes only one half of the outlet is controlled by the switch, while the other half remains powered all the time for devices such as chargers or clocks. However, electrical codes do not require switched outlets to be installed upside down.
Because orientation alone does not prove how an outlet is wired, the easiest way to check is to plug in a lamp and test the nearby switches. A flipped outlet may simply represent an electrician’s preference or a choice made by a previous homeowner.
