Assuming standard wire colors.
White: Is neutral, on your 30 amp OUTLET there should be NO voltage between the Neutral and the Safety Ground..
On the 50 amp outlet WHITE is the Center blade, this will often be a lighter color screw
Ground on both is the "Round" pin of course
That leaves the HOT lead (Black wire) on the 30 amp plug.. There should be 120 volts between the HOT and both the Neutral and the safety ground (TEST, MEasure, Do not "Believe" till you measure)
This lead goes to BOTH of the side terminals on the 50 amp outlet.
