From the looks of the photo, That adapter is for 50 amp RV's. it has a 20 amp plug and a 30 amp plug and it is junk, odds of it workig are less than 50/50.. I call it a GFCI tester (Will not work with GFCI outlets)
You can get a 15 to 50 dog bone or the Puck type adapter you ahve
These have ONE plug and ONE outlet
you can also get a 50-30 adapter that has ONE plug and ONE socket
These work,, you have limited power but they work
The 50 amp "Cheater boxes" and "Cheater cords" will not work if the outlet is GFCI protected.. I have two places I go where it will work, Just two, out of all the places I go, and one more that I've been to.
But plugging into two 30 amp outlets may get you invited to leave the park without refund.
Home is where I park it!