The Argentinian has scored five goals in seven games since his arrival from Almeria in January and a third successive win has put the Seagulls within two points of fifth-place Leicester.
Poyet said: "When you sign a player like Leo you want to show to people why you signed him.
"We didn't have the kind of player he is and his second goal especially showed his quality. He has timing, jumping and power.
"During the week he was really confident and that is the key. You have to trust your own ability and he trusts his ability, especially with heading. He really believes in what he does."
Poyet is convinced Ulloa will give Brighton an extra edge in the run-in and revealed the player himself has got the aim of playing in the Premier League.
He added: "Leo wanted to come here to help us achieve what we want to achieve. To go on and play in the Premier League you need to score a lot of goals in the Championship.
"That is the difference between this season and last season. The players know the chance we lost last year when we didn't finish well when we were fifth.
"Now there is confidence building among the players and they don't want to lose this chance again."