This is not all the uncommon. At least all you damaged was your adapter and not the shore power cord. Contributing factors:
1. Loose connection. Worn out receptacle in CG pedestal. Poor connection can cause increased contact resistance. 30 amp receptacles in CG pedestals on average get a lot more use than 50 amps due to the higher number of RVs with 30 amps.
2. Dirty connection. Caused by plugging in the shore power or adapter live all the time. The converter momentary inrush current causes pitting of the plug blades and inside the receptacle. Pitting attracts dirt which together increase the contact resistance. Never plug in live.
3. Low CG voltage along with running your AC unit. Running an AC on low voltage causes the current to increase. You can end up running at or close to 30 amps for extended periods.
It is important to note that you cannot draw more than 30 amps due to the 30 amp main breaker in your converter panel so that is not a factor.
You should periodically check the blades on shore power cords and adapters and clean with fine sandpaper. You can't check inside a receptacle or the female end of your adapter and I don't know of a way to clean pitted contacts inside either. But if the plug blades on an adapter don't look very good, the female end may be bad too.
For those with 30 amp RVs, you can use an 18" 30 amp to 30 amp extender like the Camco #55205 for under $20: This way, if you have no choice in plugging into a crappy and questionable looking CG pedestal, you will only lose the extender and not your shore power cord which could be a disaster when travelling. And again if you have 30 amps, if a 30 amp CG pedestal looks to be poor, it helps to use a 30 to 50 amp adapter because 50 amp recepts. are usually in better shape.
