Power consumption is measured in W and Wh, but what do these units mean? Water consumption can easily be understood, as we all know what a liter of water looks like. Common power meters, however, rely on the physical units or their translation to costs as display. We classified existing displays and ambient visualizations in a taxonomy that focuses on the characteristics of power consumption displays. We adapted representatives of the different categories of displays to an on-outlet display and compared these using a combination of soft- and hardware prototyping. Results indicate that ambient visualizations make it easier to understand power consumption.