What type of transformer allows two outputs to be taken from a single input?

An auto transformer is a type of transformer that uses a single winding to provide multiple voltage outputs. This is achieved by tapping into the winding at various points, which enables the retrieval of different voltage levels from the same winding. The design of an auto transformer allows for a more compact and efficient device, as it uses fewer materials compared to traditional transformers.

In contrast, a two-winding transformer consists of two separate windings that are magnetically coupled, typically resulting in one primary and one or more secondary windings. Each winding is isolated, making it less efficient in terms of space and material. A step-down transformer specifically reduces voltage from a higher level to a lower level, but it still operates based on the principle of separate windings. Lastly, a phase-shifting transformer is used to shift the phase of electrical power, rather than to derive multiple outputs from a single input.

Overall, the unique construction of an auto transformer enables it to effectively provide multiple outputs from a single input more efficiently than the types of transformers mentioned in the other options.