Psynergy Armor

A Psynergy Armor is an Armor-class bodywear available throughout the Golden Sun series.

Basic Description by Game
Psynergy Armor increases the wearer's base Defense by 21 points. Additionally, it increases the wearer's base PP meter by 20 points. As a common item, it can be bought repeatedly from Vendors for 1000 coins each and sold for 750 coins each.

In Golden Sun only one can be found in the game, in a chest in a hidden room behind a waterfall in Mercury Lighthouse, even though it is a "common" item. Psynergy Armor can be equipped by Isaac and Garet. In Golden Sun: The Lost Age, however, it is indeed sold as a common armor, in the general vendor at Mikasalla, with Felix and Piers being capable of equipping it. In Golden Sun: Dark Dawn, it is again sold as a common armor, this time in Passaj, and can be equipped by Matthew, Tyrell, and Eoleo.

Analysis
In Golden Sun when the Psynergy Armor is able to be found, it is a very useful item and a substantial upgrade over whatever armor is currently equipped. The boost to the equipped Adept's PP meter is very practical at that early point in the game, enough that it is a better piece of bodywear to equip than technically stronger pieces of armor that can be bought or found later, such as Chain Mails, which are ironically twice as valuable money-wise as the Psynergy Armor. Since it is not an Artifact, it will not appear in an armor vendor's Artifacts menu when it is eventually sold in the future.

In Golden Sun: The Lost Age, Psynergy Armor is sold commonly at the vendor at Mikasalla, which is extremely useful to the player. At that point you will most likely have found the Clothing Artifact Full Metal Vest, which has exactly the same defense rating as a Psynergy Armor. The best thing to do here is to buy one and equip it on Felix, and put the Full Metal Vest on one of the other two Adepts. Later on in the game, it is possible to acquire an even stronger armor for Felix, the Ixion Mail, but keep the Psynergy Armor in your inventory for later because when Piers joins your party later at Kibombo, he will be equipped with a Chain Mail, and the Psynergy Armor with its PP-meter boost would actually be preferable for Piers to wear over the slight defensive edge the Chain Mail would afford in comparison.

In Golden Sun: Dark Dawn, Psynergy Armor can be bought in unlimited quantities in Passaj once the shop opens. Both Matthew and Tyrell can make use of the armor, although one of the two might instead equip the Ixion Mail that can be found by that point in The Ouroboros. When Craggy Peak Ruins is reached and even better armors become available, the Psynergy Armor loses its usefulness, but it is still highly effective in the meantime.