The Power Plant is an old, abandoned building hidden near the Rock Tunnel. It can be reached after teaching your partner Pokemon the secret technique Sea Skim in Fuchsia City. The river can be found on route 10, east of Cerulean City. Surf east and south to reach the Power Plant. A Pokemon Trainer can be found outside the building.
Defeat Mark to receive P2,016 and 3 Poke Balls. Before entering the Power Plant, check the right side of the entrance to find a Thunder Stone.
Wild Pokemon will randomly spawn inside the Power Plant. You can also find wild Voltorb and Electrode by interacting with the upside down Poke Balls. The regular Poke Balls are still various items. You must defeat these stationary Pokemon in battle within 5 minutes in order to capture them.
The first item near the door is a Max Revive. A short distance further north is a Coach Trainer.
Defeat Mable to receive P4,500 and 5 Rare Candies.
Head east and south along the path until you reach a fork in the road. Take the path to the east to find a Max Potion. Search near the oil drums to find an upside-down Poke Ball which is actually a wild Electrode at Level 42! Several Voltorb candies can be found near the oil drums as well.
Return to the fork in the road and walk south to find a X Sp. Def.
Continue all the way south until you reach the southern wall. Walk east to find a Rare Candy near a generator.
Head back to the main hall and take it to the southeastern side of the building. TM38 Thunder can be found in this small room. This is the strongest electric-type attack in the game. An Electrode can also be found in the corner of this room.
Return to the main hall and walk to the northern room. A Thunder Stone and a Max Potion can both be picked up here.
Follow the main hall to the west. You can pass up one Electrode and follow the path to the south. Another Electrode will be in a small room next to a Paralyze Heal.
The legendary Pokemon Zapdos can be found to the west. He is the second of three legendary bird Pokemon in Kanto. Make sure you save your game before interacting with the Pokemon. If you fail to capture it, defeat it in battle, or you want a different nature, you can restart the save file and try again.
Before you get the chance to capture Zapdos, you must fight and defeat the Pokemon within the five minute time limit. Use either ice- or rock-type attacks to deal massive damage and defeat it quickly. The Rock Slide you obtained near the entrance will prove useful here. Once you get the chance to capture it, Zapdos will create an electrical storm that zaps any berries you throw. Wait for the electricity to subside or throw a Poke Ball instead.
When you’re ready to continue, you can exit out the building through the door to the west.