RV:
You can get it at Crutchfield:
https://www.crutchfield.com/p_703NRGX210/AudioQuest-NRG-X2-10-ft.html
The three prong plug is used to connect the equipment ground to earth ground and, for ungrounded appliances, to make sure the correct polarity is fed to the appliance. A C-17 plug is used for non-grounded non-polarity appliances so you don't need the third prong.
You can get it at Crutchfield:
https://www.crutchfield.com/p_703NRGX210/AudioQuest-NRG-X2-10-ft.html
The three prong plug is used to connect the equipment ground to earth ground and, for ungrounded appliances, to make sure the correct polarity is fed to the appliance. A C-17 plug is used for non-grounded non-polarity appliances so you don't need the third prong.