An apparatus for coupling power systems, in particular a DC system, for example a motor vehicle electrical system, with a single-phase AC system or a further DC system, the apparatus including a non-inverting DC-DC converter and an inverting DC-DC converter, each having a first input and/or output and a second input and/or output, the first input and/or output of the first DC-DC converter being connected in series to a first converter valve to form a first series circuit, and the first input and/or output of the second DC-DC converter being connected in series to a second converter valve to form a second series circuit, the first and second series circuits being connected in parallel, and the second inputs and/or outputs of the DC-DC converters being connected in parallel and the terminals of the parallel circuit of the series circuits being connected to a first input and/or output of the apparatus.