This setup is especially common in bedrooms and living rooms that were built without permanent ceiling lights. Instead, builders provided a switched outlet where homeowners could plug in a lamp. Flipping the wall switch would then turn the lamp on or off just like a traditional ceiling fixture, and installing the receptacle upside down made the switched outlet easier to identify.
Sometimes only one half of the receptacle is connected to the wall switch, while the other half remains powered all the time. This allows a lamp to be controlled from the switch while devices such as clocks, chargers, or routers remain continuously powered. However, there is no national electrical code requiring switched outlets to be installed upside down.
Because of that, an upside-down outlet does not automatically mean it is switch-controlled. Some electricians prefer that orientation for other reasons, while in other homes it may simply reflect the preference of a previous owner or installer. The easiest way to find out is to plug in a lamp and test the nearby wall switches—you may discover that an outlet you thought was dead is actually working exactly as intended.
