This invention relates to a transformer (1) for multi-output power supplies such as those commonly found in electronic equipment. The transformer comprises a magnetic core (3) and a plurality of windings (5, 7, 9) at least some of which are fractional windings, arranged about the magnetic core. The transformer comprises a dual transformer structure with a pair of transformers, a main transformer (11) and an auxiliary transformer (13). In a preferred embodiment, the main transformer and the auxiliary transformer are connected together. In this way, readily available magnetic components may be used in the construction of the transformer and the simple construction allows for a large cross-sectional area of transformer to be deployed so that reduced turn counts of windings may be used.