Mike In NY, The EMS detects a 50 amp connection by looking at the voltage difference between the two in coming power wires. If the difference between the two hots is 0 VAC it assumes both lines are the same. This is what the 50 amp to 30 amp pigtail does, ties the two hots together then you select 30, 20 or 15 amp service.
When connected to a true 50 amp service there will be 240 VAC difference between the two hots.
I assume you are plugging into a 120 vac 20 amp normal wall receptacle. Looks like attached picture.
Grant & Pat
2014 Adventurer 35P
2012 Jeep Wrangler Rubicon