"The gaffer came to watch me and was interested in me, so I came down," Capaldi told the Plymouth official website.
"It's a great little set-up, the team plays football and are a good bunch of lads, some good players. The fact they wanted me to come down and sign so quickly was a big appeal.
"It's definitely now the time to start playing first team football. I've played reserves for the last four seasons. I've played a few too many games for the reserves and I'm looking to get a couple of first team seasons under my belt and take it from there.
"I've been looking at a few clubs and this one really stood out. It's a really promising club with a big future, hopefully."
Capaldi was told by Blues last week that his contract would not be renewed when it ran out in the summer and he moves to Home Park as a free agent - we wish him well!