Hi Matt and welcome to the forums.
What types of fixtures are you plugging into the controller? You say 4-8, but each of those lights might be 2000w a piece (doubtful). The other thing is it is possible the outlet is a 15 amp outlet and not a 20 amp outlet. According to standard, 20 amp Edison has one on the prongs at a 90 degree angle with regards to the other. See this image for what exactly I am talking about.
Almost no one follows this standard, but it is possible, especially in newer buildings since there has been an up rise/appearance of such plugs and outlets in recent years.
Once again welcome to the forums.