You will find that in general, 50 amp receptacles are in better condition and thus a better choice anyway. 30 ampers get rather abused in comparison. Look closely at some 30 amp recepts. and they will be blackened and crispy which can lead to overheating. At one CG last year, they had all 30 amp pedestals and they were all in really bad shape, so bad that I had to use a stick to keep the plug from falling out and kept the load to a min. to reduce risk of overheating.
If in a section with 50 amp pedestals, the cable between pedestals will be much heavier gauge and you are more likely to get better voltage. We were at one CG this summer where the 30 amp pedestals were only 106 volts. Moved to a section with 50 amps and got 117-118 volts.
The panel in a TT has a 30 amp main breaker in it so plugging into a 50 amp pedestal is fine.
If you are at a pedestal with 30 & 50 amps and the 30 looks iffy or is loose, use the adapter. Don't forget to always turn the pedestal breaker off before you plug in.