Modem and router not working very weird?

My wireless has always worked after moving my modem and router to a different cable outlet in the apartment, and I know all cable outlets work. However, if my modem and router are plugged into this one particular electric socket where both are definitely receiving power (lights flash on the Insight modem and router), my network is identifiable but wireless does not work. From this electric socket I have connected the modem to multiple cable outlets (I have long cable wires), and the internet still had the same problem. As soon as I switched to a different electric socket though, wireless works perfectly, no matter which cable outlet it's plugged into. WTF?!