The Power Plant is located in the middle of Route 10—you have to go through the Rock Tunnel, then up Route 10 to the water, where you can Surf back down Route 10 to the building below the Rock Tunnel exit. Assess the situation at the Power Plant and try to fix it, or you won't get much farther.
The power is out for all of Kanto because someone swiped a part from the Power Plant. As you leave, a guard will give you a tip that a suspicious character has been spotted in Cerulean City, which is west through Route 9. But before you go to investigate, search the strip of grass outside of the Power Plant (that's Route 10) for an Electabuzz.
Electric-types are few and far between, so good ones like Electabuzz are always welcome. Its Speed and Special Attack scores are top class, and it should already know Thunderpunch but the time you get it. At later levels it now learns Thunderbolt as well as Thunder, and it will bear new Pokémon Elekid if you breed it!