Benitez, who coached Liverpool for six years and Chelsea for one, oversaw the latter's elimination from the League Cup by Swansea last season, and the Spanish tactician said his experience of coaching against the Welsh club is one positive for Napoli ahead of their last 32 first leg on Thursday.
Swansea will host the Serie A side at the Liberty Stadium.
"Obviously they have changed now their manager and it is different," said Benitez, comparing the current Swansea side to the team he coached against.
"I know the players and I know the style, you have to explain to your players.
"For me, because you will play against a team of the Premier League, that is the real challenge for us."
Benitez led Chelsea to Europa League glory last season and considers the second-tier European competition as important for Napoli but conceded it may not be top priority for Garry Monk's Swansea side.
"To see a team in the middle of the table, I don't know if they will be thinking about Europa League or maybe keeping an eye on the bottom of the Premier League and see the dangers," the 53-year-old Spaniard said.
"We will see tomorrow, but for us, it is a challenge to play against a team like this and the advantage is because we know how they play but in the end it has to be the players on the pitch."
Benitez said the varying motivation of their rivals in the competition made it all the harder to win.
"Obviously winning in the cup and winning a trophy is always an important thing to achieve," he said.
"However winning is never easy and the Europa League is a very difficult competition to win because not everybody understands the importance of winning or the importance of not winning.
"You have to know the team you are playing against and for example I know Swansea and that is an advantage because I can tell my players that Swansea is a very difficult team to play against.
"They are organised and play good football at a high tempo. The fact that they will play against Napoli, who are possibly a better team, will only galvanise them and their performance."
