Location and Uses
The Faces of Evil
The Power Sword goes unnamed in The Faces of Evil. It is a stronger Sword that allows Link to fire Power Blasts when he is at full health. Link receives the Sword from Anutu in Crater Cove after correcting him that the crab he caught is actually a Gohma.
Later in his quest, Link can have his Power Sword upgraded into a stronger form that allows him to fire Power Blasts at any time, even when he is at low health. Link has his Sword tempered into this form after freeing Kulvan in Shipwreck Cliff and giving him a Fire Diamond. In its in-game cutscene, the Power Sword is shown to have become very powerful, capable of shooting devastating, explosive Power Blasts.
The Wand of Gamelon
In The Wand of Gamelon, the Power Sword appears identically as in The Faces of Evil, allowing Zelda to fire Power Blasts when she is at full health. Zelda finds the Power Sword inside of a dark house in Sakado inhabited by Moblin Spearthrowers and Keese.
The Power Sword can also be upgraded into a stronger form that allows Zelda to fire Power Blasts at any time. Her Sword is tempered into this form by Yokan in Sakado after bringing him a Heat Crystal.