Abstract: The present disclosure relates to a transformer with a modular design, the transformer comprising: a front-end assembly comprising an input electrode for receiving an input voltage; a back-end assembly comprising an output electrode, for outputting an output voltage converted by the transformer; and a magnetic core, the magnetic core being configured to assemble the front-end assembly and the back-end assembly together. The back-end assembly comprises one or more conversion modules, each conversion module being capable of independently converting the input voltage into the output voltage in collaboration with the magnetic core, and the power of the transformer is the sum of the power of all the conversion modules. The present disclosure further relates to a direct current-to-direct current converter comprising such a transformer, a vehicle comprising such a direct current-to-direct current converter, and a method for assembling such a transformer.