Tamper Resistant Outlet Can T Plug In . They have the letters tr stamped on the face of the receptacle. Apr 13th, 2010 4:28 pm. . ShockShutter Tamper Resistant Outlet Cover Review from just10moreminutes.blogspot.com First of all, try to keep the plug straight. Secondly, try to push the largest blade in first. Never try to modify or widen a tamper.