Every time someone in my server kills a wild pokemon while they have a Power item equipped (Power Band, Power Anklet, Power Lens, etc.) they gain the evs dropped by the wild pokemon, BUT they also add 8 evs onto their evyield continuously. Ex. If someone killed a wild Charmeleon with a Power Anklet item equipped the wild Chameleon would gain 8 speed EVs. It's always 8 evs added onto the wild pokemon, and even if a pokemon has 0 evyields in a stat it would gain 8 evyields depending on the item equipped. Ex. Power Weight always increases Evyield HP by 8, Power Bracer increases Atk by 8, etc.

There's also a case where a geodude's stats just shot up drastically, which I attached.