A couple of things to note:
1) amps are "pulled" by the devices being used,not pushed by the source.
2) 50amp service is two legs of 50amp each. (reason for 4 prongs, not three) for a total of 100amp available to be "pulled".
3) Using a 30amp adapter only pulls amps from one of the two 50amp legs if attached to a 50amp service (it also limits you to 30amps).
4) your available amps are limited to the lowest rating in the power stream, be it at the source such as 50, 30, 20 or 15amp recepticle, any adapters being used with similiar ratings, or an extention cord.
5) converters, electric hot water heaters, and refrigerators set on electric are often overlooked as amp pullers and come on randomly so
the issue can appear to be sporatic.
6)I am not an electrican but the above simplifies it for me and keeps me out of harms way.