TL/DR: They don't reject electricity or any other technology outright. They pick and choose the technology that will benefit them, and reject anything they feel is detrimental.

Long version: There's many flavors of Amish, and all follow different rules. Technology is allowed or forbidden depending on its impact on the community. Telephones? Some communities love them, it brings distant neighbors together. Cellphones? Yes, for the same reason. A smartphone that lets you spend all day scrolling Reddit, that's probably not going to fly because it'll separate you from your community rather than bringing you closer.

And there's also rules for what's allowed at work. A friend of mine bought a trailer from a PA company, and she was surprised to see Amish people driving forklifts, running power tools, arc welding, etc, as part of the manufacturing process. The Amish aren't held to the same standards when on the job, because doing so would make them unemployable.

So yeah, it's not as simple as it seems, and every community is a little different.