New 5th Wheels & (30amp receptacles)
All RVs (which use AC) are 110 volt. They typically come in 3 amperage flavors. 15 Amp (the usual plug in your house, generally for very small RVs, or those without AC), 30 amp (3 big prongs, usually on RVs with 1 AC unit) and 50 amps (4 big prongs, usually on the biggest RVs, with 2 or more AC units). 15 amp sockets are almost always dual sockets, which are tied together for a TOTAL of 15 amps between the 2 of them. Be aware of this if anyone is using the other socket of the 2. 30 and 50 amp sockets are usually single and individually fused to their full rated amperage.
As rvwizard says, you can check your trailer near the cord (or see the rating on the main circuit breaker) to find out what your trailer takes. Not every park offers every amperage, so you will want adapters to plug whatever you have into one or both of the other two types of socket.
For instance, my trailer is 30 amp, and I have plugged it into a 15 amp outlet (using an adapter) and started the AC (but ONLY the AC) with good results. I can also run everything else EXCEPT the AC from 15 amps. Obviously, my best choice is a 30 amp socket, if available. If not, a 50 amp socket with adapter would be quite fine. As a last resort, a 15 amp socket with adapter will do, as long as I watch my current usage.
If your trailer is rated 50 amps, you can, of course, plug into a 30 amp socket (with the appropriate adapter) but you will have to watch your current usage - only 1 AC at a time, etc. Although it is technically possible, I would not advise plugging a 50 amp RV into a 15 amp socket. Note, however that they do have a device available, which allows you to plug a 50 amp RV into 2 30 amp sockets, or a 30 amp socket and a 15 amp socket, and get essentually full usage. This probably only works because both sockets you plug into are separately fused.
By the way if you 'don't like' the plug which comes on your RV, don't think you can just change it to one you do like. Usually this requires significant rewiring of some or all of the RV, especially the fuse box.