Comfort Zone is the company that makes Feliway (and also the dog one, DAP). I have had dusty smelling ones before, and I cleaned off the plastic holder part and it helped. They always have a slight smell to me, though, if I'm right next to them. You might want to try plugging into a different outlet and see if that's better. I had a faint burning smell in my room once that I traced to (as I thought) an air freshener plug-in, but when I unplugged it, I found it was actually the outlet that needed to be replaced. So I'm always nervous about that now! They also make a spray version of Feliway, if you can't get the plug-in one to stop smelling.
ETA: I was just reading an article from Best Friends animal society, and they mention using these calming collars in their sanctuary for stressed cats: http://www.amazon.com/NurtureCALM-Feline-Calming-Pheromone-Collar/dp/B00460Y17S