Our 320RS came with 50 amp and a 25' shore power cord and our first trip out...the electric outlet was about 29' from the back of the trailer. So - fortunately, we were within 20 miles of Camping World and we now tote a 20' or 25' (can't remember) 50-amp extension cord.
And surprisingly, we have had to use it. I never bothered to measure the power cord on our previous RV (Sandpiper fiver) - but we NEVER had issues.
Oh...one other thing we bought that came in handy last week. We frequent a spot where 50-amp plugs are rare, so I had ordered from Camping World...an adapter that uses two 30-amp plugs to give you 50-amp power.
50-Amp RV Box Adapter - Intersource Enterprises D11-136 - Electrical Adapters - Camping World
Worked flawlessly and it's a good investment since we visit this spot once a month year-round for a week.