Equipping the Energy Amplifier will allow your Unite Move to charge faster than usual. This includes a greater effect when doing actions that fill up your gauge (defeating Pokemon, scoring), as well as passive gauge gain when doing nothing. Check out the list below to find specific reduction timings for the item at level 20 and 30 respectively.
Charge Times For All Pokemon
The times noted here are based off of equipping the Energy Amplifier & doing nothing else until the Unite Move Gauge completely fills up.
All Other Pokemon
Damage Boost Lasts 3 Seconds
After using your Unite Move, the Energy Amplifier will provide you with a brief boost in damage. This will last a total of 3 seconds. Ensure that you use your Unite Move carefully to make the most use of these 3 seconds possible.
Effect By Level
After the Pokemon uses its Unite Move, the damage the Pokemon deals is increased by 7% for a short time.
After the Pokemon uses its Unite Move, the damage the Pokemon deals is increased by 14% for a short time.
After the Pokemon uses its Unite Move, the damage the Pokemon deals is increased by 21% for a short time.