The invention relates to a transformer for a DC-DC converter, in particular a resonant converter. The converter comprises a transformer unit (35) which comprises at least one winding (31, 33) with a first winding connection (35-1) and a second winding connection (35-2) and a capacitor assembly (34) consisting of at least one capacitor (34i) with a first capacitor assembly connection (34-1) and a second capacitor assembly connection (34-2). The capacitor assembly (34) is arranged so as to lie against the transformer unit (35) in order to form an assembly. The capacitor assembly connections (34-1; 34-2) are connected to the winding connections (35-1; 35-to) via one or more first connection parts (343) in a specified manner with respect to the electric connections. The capacitor assembly connections (34-1; 34-2) and/or the winding connections (35-1; 35-2) are electrically connected to multiple second connection parts (360; 363) in a specified manner with respect to the electric connections for connecting to a first and a second power module (11M; 12M).