Wand, rare
"a wand with a space for a large diamond on the end"
When you insert a diamond worth at least 500 GP, the wand gains 3 charges.
You can spend an action to use a charge and duplicate one item within a 20-foot radius. The duplicator cannot duplicate magic or life, so if you attempt to duplicate a creature, the duplicate will be dead.
I could see a player amassing, say, 10,000gp and one 500gp diamond, put the gold in a massive chest, use the wand 3 times, each time transfering all the gold into the original chest and end up with 80,000 gold in a massive chest, and three empty massive chests, and then buy another diamond for 500gp and repeat for as much as the massive chest would hold.