Originally Posted by Elite Dialga
Actually, the amount of ev's gained are doubled
because of the item held (respective item) or macho brace (for all types of evs), say a pokemon gains 2 EV's by defeating a pokemon would get 4 isntead of 2, if its holding such an item. There are no fixed EV's that are gained due to these items.
No that's not true.
Any Power Item add +4 EV's on any EV's you've gained that battle.
Only Macho Brace and Pokerus will double the amount of EV's given.