actually i think that you get +4 only when you level up your pokemon
example
you are fighting an abra but you DONT level up. you just get 1 EV in sp attack
you are fighting an abra and you DO level up. you get 1 ev+4ev in sp attack
Power items sorry. Anyway, they make it so you get the usual amount of EVs plus 4.
For example: I buy the Power Lens, which gives me 4 Sp. Atk EVs. I go and fight a wild Abra, it will give me 5 EVs instead of 1. Combine that with Pokerus, and you can EV train in a matter of minuetes!