Robbbyr posted links to some very good reading on the subject.
The 50-amp 120/240-volt 3 pole 4
You are correct that a 30 amp RV plug is going to give you 3600 watts of power. 30x120=3600
A 50 amp RV plug is going to give you 12000 watts of power.
L1 50 amp x 120 vac =6000 watts
L2 50 amp x 120 vac =6000 watts
Technically it is not 100 amp it is 50 amp twice.
Lets say I have my 50 amp trailer plugged into a 50 amp RV service.
My EMS reads
L1 120v 50amp
L2 120v 50amp
I'm using 6000 watts of power on L1 and 6000 watts of power on L2 for a total of 12000 watts.
If I take a clamp on amp meter and check the Black wire on L1 I will have 50amp. Put the meter on the Red L2 I will have 50amp.
Put the meter on the White Neutral I will have 0.
It is Alternating Current
I hope this helps.