The American forward spent the 2009-10 season on loan at Hull City, struggling to only one goal in 28 league appearances as the Tigers were relegated.
His fortunes have changed in recent years, however, with the 23-year-old having 63 appearances in all competitions for Eredivisie side AZ, scoring 45 times, and Altidore feels that he returns to England an improved player.
|200/1||Jozy Altidore is 200/1 with Bet365 to be the Premier League's top scorer
"On and off the ball and linking up with the players around me, I just got better. It's that simple. I've become a much more confident player since then."
Altidore is one of nine players signed by Paolo Di Canio so far this summer, as the Italian looks to improve on his side's 17th-place finish in the last campaign, and the striker believes that the firepower within the squad can ensure success at the Stadium of Light.
"[Stephane] Sessegnon is a top, top player. There's no doubt about it," he enthused, "and Connor [Wickham] is a very good player too.
"I think we have a lot of good options there and hopefully [Steven] Fletcher will be fit soon too."