Im sure there is a more advanced way to do it but I did a test with a scene.
Maybe others have a better idea or method, will help you
I created 2 x scenes with the following rules
Scene 1. When Plug 1 = on then Plug 2 = off
Scene 2. When Plug 2 = on then Plug 1 = off
what this did for me was when i turn on Plug 1 then the plug 2 goes off and when plug 2 goes on then plug 1 goes off.
Im sure there must be a method with scripting or some other rule i am not sure of but hope this helps