The item you linked has the normal 50amp RV male parts but the female parts are different. Most 30amp RV cords plug into a TT30R outlet (at least that is what mine does). Which looks like this. I'm guessing the male part of your 30amp power adapter would be the TT30R.

So the power cord coming from your RV has the wrong male parts. You can keep the 50 to 30amp adapter you will just need to add one of these.