I would guess none as it wasn't a lack of confidence which made him have no aptitude to run or even stand in the right place, or have a body shape completely unsuitable for a top level footballer, or show precisely no technical skills at all. At very, very best he's a very, very crude battering ram against opponents susceptible to such crude methods. A very low rent Emile Heskey circa 2001.
Sunderland should have known all that before they signed him and one goal would have made no real difference. He ended up with a record of 4 goals in 80 games in English football, it tells its own story. He was horrendously out of his depth at Hull and you could tell after about two games at Sunderland that he wasn't any different four years on. For reference Glenn Murray who is the archetypal limited trier has just overtaken Altidore in terms of Premier League goals, in a fairly poor team (in terms of quality, probably no better or worse than Sunderland), from a fraction of the games played.
