I've always gotten the impression that the capital accent is the equivalent of a 4-year-old trying to tell you an exciting story anyone else feel that way
From the text we can infer that the Capitol accent is upbeat and exaggerated;
Suddenly he falls into a Capitol accent as he mimics Effie Trinket, the maniacally upbeat woman who arrives once a year to read out the names at the leaping.
Besides, the Capitol accent is so affected, almost anything sounds funny in it.
“Sorry!” she pipes in her silly Capitol accent. “You’re just so hairy!”
The Hunger Games
