I used the 30-50 wishbone adapter off and on for many years. You won't be able to necessarily draw 50 amps, but you usually can get more than 30 amps. With the straight 50-30 amp adapter you are drawing both legs off the 30 amps. With the 30-50 amp wishbone adapter you are drawing one outlet off the 30 amp and the other off the 20 amp plug . I tried to put the leg that used the most electricity, like the ac, on the 30 amp plug and the other leg on the 20 amp side. Had a voltmeter in the camper that I used to watch the draw.
Roger & Cheryl Full Time since 2002, RVing since 1975 2008 Chevy 3500 Crew Cab Dually, 2012 RW 36RL