I've only seen EmPower on planes.

The Radio Shack guy is almost right. You do need two items. The cigarette lighter adapter cable/ADAPTER sits between your laptop's power brick and the EmPower-cigarette lighter adapter.

The EmPower-cigarette lighter adapter is universal. The power brick end of the cigarette lighter adapter cable/ADAPTER needs to fit your power brick.

I wrote ADAPTER in cigarette lighter adapter cable/ADAPTER because this "cable" might come attached with its own power brick. Depending on what model laptop you have, you actually have two power bricks sitting between the seat and your laptop.