Per player character max caps:25,000 caps
Earn max caps per day:1,400 caps
A single trading max caps:5,000 caps

The limit of Bottle Caps in Fallout 76: Per player character can possess a maximum of 25,000 caps in the Fallout 76 game. You can earn max 1,400 caps per day. Moreover, there is a 5,000 caps limit per item when trading with other players.

Fallout 76 just wants to spend the caps instead of saving it. From my experiences, I owned several characters in Fallout 76: one main player account and several alternative accounts to store more caps.