Psych Up copies both the positive and negative changes to the target's stats and replicates them onto the user. The target's Attack, Defense, Special Attack, Special Defense, Speed, accuracy and evasion are copied. Any changes made to the target's stats after Psych Up is used will not affect the user's stats.
So it will copy any boosts for the ability, but any boost after you used Psych Up will not be received. Although you can just use Psych Up once again.