15 AMP / 30 AMP / AND 50 AMP
is what you usually run into in campgrounds here in the good old USA
What you will probably want on hand is one of these......
http://www.amazon.com/Conntek-Male-Female-Connector-Adapter/dp/B00268WS72/ref=sr_1_2?ie=UTF8&qid=1323199608&sr=8-2
about 5 bucks +/- and simply toss it into the junk drawer. Mine has saved me a couple of times. Get settled in and find the 15 - 20 amp line on the service mast has a bad breaker what's a guy to do. You can simply adapt over the 30 amp "Y" shaped plugin to accept your extention cord.
Now, just because you have moved up doesn't mean you can fire up your welder, or run 4 - 5 heating element appliances. Your trailer is still the limiting factor but you can now have lights and electric even if the breaker on the 15 / 20 amp side is fried.
In cold weather I have ran the 1500 watt heater off of the 30 amp terminal
on a seperate cord. (1500 watts IS 15 amps, this means you would have been tapped out on the 15 watt side) This set up leaves capacity enough to allow the trailer circuits to supply the necessary wattage to run coffee makers, microwaves, or toaster ovens on the 15 / 20 watt service side "if it's working" without competing with the much needed heater.
It's always good to have a back up plan!