Disclosed is a method of supplying power to a building equipment technician in the field. The method comprises providing a movable power conversion device having a transformer, an input voltage selector, a building power interface cable, and a power receptacle. The method further comprises moving the movable power conversion device to a location proximate a building power grid and an area comprising building equipment; setting the input voltage selector to an unpowered position; connecting the building power interface cable to the building power grid; and selecting a supply voltage of the building power grid with the input voltage selector.