Electrical assembly comprising an installation comprising an alternating current power supply port and at least one electrical system (14 1,..., 14 n), and a device for supplying without interruption the power supply port with alternating current, the uninterruptible power supply device comprising: - a first circuit for electrically connecting the power supply port of the installation to an alternating current power supply network, - a back-up device, comprising a rectifier, means (44, 46) for charging, storing and discharging electrical energy and an inverter, connectable to the power supply port of the installation, wherein the back-up device is arranged in a second alternating current supply circuit connectable to the power supply port in a by-pass of the first circuit, the uninterruptible power supply device comprising a switch arranged and commanded by a controller to connect selectively the first or the second circuit to the power supply port, characterized in that: - each electrical system (14 1,..., 14 n) of the installation consumes direct current and is electrically connected to the power supply port through a direct current power supply device (26 1,..., 26 n), with AC/DC conversion, - the installation comprises at least one module (30 1,..., 30 n) for managing the direct current power supply of the electrical system (14 1,..., 14 n) by the direct current power supply device (26 1,..., 26 n) with AC/DC conversion, this management module (30 1,..., 30 n) being designated to transmit an information message (N-OK) on the state of the direct current power supply of the electrical system (14 1,..., 14 n) to a controller of the switch, and - the controller is designed to command the selective connection, by the switch of the first or the second circuit to the power supply port as a function of the state of the supply with direct current of the electrical system (14 1,...,14 n) as indicated in the information message (N-OK) transmitted by the management module (30 1,..., 30 n). - a first circuit for electrically connecting the power supply port of the installation to an alternating current power supply network, - a back-up device, comprising a rectifier, means (44, 46) for charging, storing and discharging electrical energy and an inverter, connectable to the power supply port of the installation, - each electrical system (14 1,..., 14 n) of the installation consumes direct current and is electrically connected to the power supply port through a direct current power supply device (26 1,..., 26 n), with AC/DC conversion, - the installation comprises at least one module (30 1,..., 30 n) for managing the direct current power supply of the electrical system (14 1,..., 14 n) by the direct current power supply device (26 1,..., 26 n) with AC/DC conversion, this management module (30 1,..., 30 n) being designated to transmit an information message (N-OK) on the state of the direct current power supply of the electrical system (14 1,..., 14 n) to a controller of the switch, and - the controller is designed to command the selective connection, by the switch of the first or the second circuit to the power supply port as a function of the state of the supply with direct current of the electrical system (14 1,...,14 n) as indicated in the information message (N-OK) transmitted by the management module (30 1,..., 30 n).