Pedestals are the same as a panel in a house. There are 2 hots and a neutral and are usually 125 amp or 200 amp mains and can be configured with receptacles & breakers to suit the specific installation. The stolen diagram above shows how they are wired inside. Pedestals nowadays are loop fed from one to the next. The photos below show a typical 50/30/20 amp pedestal inside and has feed-through lugs for heavier cable for loop-feeding to the next pedestal. Note the small gauge wire from the feed-through lugs to the breakers.
If you are using an adapter to get 30 amps from a 2P-50 amp receptacle, the most you could draw is 30 amps. Then if you also used an adapter to get 15 amps from a 30 amp receptacle, the most you could draw on that circuit would be 15 amp. As mentioned above, the most you would draw is 45 amps at (120 volts). This should not cause a problem as far as demand load goes according to the NEC.
As an example, say a feeder is supplying a run of 50/30/20 amp recepts. and 200 amp pedestals are used, a max. of 9 pedestals is allowed by the NEC and the breaker for the feeder would be 200 amps (2 pole). The NEC requires a min. demand load of 9600 watts per 50 amp recept. (2P-40 amps) and for a run of 9 pedestals, a total demand factor of 55 percent is then applied to that so the code is thus providing for 9 pedestals running at 55 percent x 9600 watts = 22 amps per pedestal (or equiv. of 44 amps at 120V). Your draw of 45 amps should not have an impact on that pedestal or others on that run.
If you want a little extra power, why not just plug directly into the 15/20 amp GFCI recept.? That way you'd eliminate the need for an adapter and also, 30 amp recepts. can sometimes be very tired, abused and crispy looking and don't make a good connection.
