The Enchanted Diamond Armor Chest is a trick loot chest in some CTM maps by Vechs.
Despite the name of the chest, saying it contains Enchanted Diamond Armor, it usually only contains a raw fish. Vechs often places this chest in dangerous places - for example, the entrance to Black Heart Citadel in Spellbound Caves used it to lure the player into a trap, and in Waking Up it is at the end of a Nether brick fence bridge.
This was originally intended to be a stack of 0 diamond armor, but by splitting the stack, you could get infinite Protection III diamond armor.
In some versions of Waking Up (most notably, version 3.6.5), the chest contains full Protection III diamond armor, with the boots having Feather Falling III and the helmet having Respiration III. In the Spellbound Caves developer commentary, Vechs edited his map to put real diamond armor in the chest and disabled the nearby trap in order to troll anybody watching the video before playing the map; his refusal to actually equip the armor served as a subtle hint that not was all as it appeared.