To add to what Steverino says, I would mention that this EVSE would be important to any 2011/2012 Volt owner who needs to charge at the 8 amp L1 level because you can't do that from within the car. The default for the 2011/2012 Volts was 12 amps (default was changed to 8 amps starting with the 2013 Volt), and there was no option to change that from the car’s center console touch screen display. The buttons on the EVSE itself provide the opportunity to set it for what the manual describes as Normal or Reduced level (12 amp/8 amp).
Another selling feature is there should be a flashlight built into the vehicle plug that can be used by squeezing the vehicle plug lever. The flashlight will turn off when the connection is complete and the lever is released.
You can’t change the level via the buttons while the EVSE is plugged into the car’s charging port (set the level before plugging into the car), but I know from doing so last September for my 2012 Volt that if you set it to the Reduced 8 amp level, it will remain at 8 amps for multiple charging sessions if the EVSE itself remains plugged into the wall socket. I don’t know if it "resets itself" to the 12 amp default when you unplug it from the wall, or if it remains set at the 8 amp level until you press the buttons again. Anyone buying this to use for 12 amp L1 charging should be sure all 4 lights are lit when using it (i.e., I don’t know if you could use a 2013 or later Volt’s touch screen to choose 12 amps for the session if the EVSE was set via the buttons for 8 amp charging).
As for why the 4 lights, perhaps they do indicate 6/8/10/12 amps... it could be this EVSE was also used for the Ampera in Europe. Some old threads I found some time ago included these posts:
"The on board charger is the same, the UK portable ESEV is limited to 6 amps as the typical home circuit for 220V is 10 amps."
"Charging options in the UK are 230V at 10A (or less if you really want) from a standard mains socket, or a dedicated 16A or 32A charger. (UK voltage is a nominal 230V but usually about 240V in practice.)"
" It's true, that Ampera's mobile EVSE has a button, with which I can select 10A or 6A charging (EU - 230V)..."
Don’t know why the title of this posting refers to a Bolt ("Chevy Bolt Voltec Charger GM Chevrolet Volt EV Electric car Charging station 12A").