Most ( I think really all do) power panels pulse a full 12 volts to the plug. Nominally, it puts the full 12 volt battery voltage on the plug for 1 millisecond then nothing for the next 9 milliseconds. When you turn that dial, you are increasing or decreasing that 1 millisecond time period. Now, if the source voltage changes, the equivalent average voltage applied to the plug also changes and can cause plug burnout as noted above.