In the Golden Sun games, there are items that you can equip to Adepts to have them use new Psynergies. These new Psynergies are almost entirely utility Psynergies. These are the items that you can equip to receive new Psynergy.
“Several pieces of equipment in both games in the series bestow not power or statistic boosts...List of Utility Psynergy items
“The Tomegathericon is an item in Golden Sun: The Lost Age. It appears to be a black book with...Tomegathericon
“The Mysterious Card, Found in the Kandorean Temple, is the first class-changing item found in...Mysterious Card
“The Trainer's Whip is the second of three Class-Changing Items acquired in The Lost Age, and is...Trainer's Whip
“The Hover Jade, also referred to as the stone of Yegelos, is a stone given to Felix and his...Hover Jade
“The Class-Changing Items are introduced in Golden Sun: The Lost Age. When one of these items are...Class-Changing Items