It's common practice to place a supercharger cable over the top of the charger if a particular stall is out of order. The goal is to save other people from backing in and then realizing it's not working.
The display currently shows how many stays are working, but it doesn't show you which stalls are out of order.
Suggestion: show which stalls are out of order right in the display.
Bonus: see related ideas about simply suggesting the best stall to use.