Method for managing an electrical power supply system of an aircraft, the power supply system comprising: - at least two distribution bus (ACBUS1, ACBUS2, DCBUS1, DCBUS2) arranged so as to power electrical loads, the distribution buses belonging respectively to a right-hand portion, said first portion, and a left-hand portion, said second portion, of the power supply system; - at least one generator (G1, G2) of a propulsion engine of the aircraft which is capable of providing a supply of electrical energy; - a first engine-class main power unit and a second engine-class main power unit which are capable of providing a supply of electrical energy, the first engine-class main power unit and the second engine-class main power unit respectively supply the distribution bus of the first portion and the distribution bus of the second portion of the power supply system during normal operating conditions of the aircraft; - a plurality of contactors (C1-C18) which are capable of electrically connecting the distribution buses (ACBUS1, ACBUS2, DCBUS1, DCBUS2) to the propulsion engine generator (G1, G2) and/or the first and second main power units (MPS1, MPS2); and - a management module which is capable of controlling the contactors (C1-C18); method wherein: - during normal operating conditions of the aircraft, the management module controls the contactors (C1-C18) so as to power the distribution buses (ACBUS1, ACBUS2, DCBUS1, DCBUS2) using the first and second engine-class main power units (MPS1, MPS2) and - during back-up operating conditions of the aircraft, the management module controls the contactors (C1-C18) so as to power the distribution buses (ACBUS1, ACBUS2, DCBUS1, DCBUS2) using the propulsion engine generator (G1, G2). - at least two distribution bus (ACBUS1, ACBUS2, DCBUS1, DCBUS2) arranged so as to power electrical loads, the distribution buses belonging respectively to a right-hand portion, said first portion, and a left-hand portion, said second portion, of the power supply system; - at least one generator (G1, G2) of a propulsion engine of the aircraft which is capable of providing a supply of electrical energy; - a first engine-class main power unit and a second engine-class main power unit which are capable of providing a supply of electrical energy, the first engine-class main power unit and the second engine-class main power unit respectively supply the distribution bus of the first portion and the distribution bus of the second portion of the power supply system during normal operating conditions of the aircraft; - a plurality of contactors (C1-C18) which are capable of electrically connecting the distribution buses (ACBUS1, ACBUS2, DCBUS1, DCBUS2) to the propulsion engine generator (G1, G2) and/or the first and second main power units (MPS1, MPS2); and - a management module which is capable of controlling the contactors (C1-C18); - during normal operating conditions of the aircraft, the management module controls the contactors (C1-C18) so as to power the distribution buses (ACBUS1, ACBUS2, DCBUS1, DCBUS2) using the first and second engine-class main power units (MPS1, MPS2) and - during back-up operating conditions of the aircraft, the management module controls the contactors (C1-C18) so as to power the distribution buses (ACBUS1, ACBUS2, DCBUS1, DCBUS2) using the propulsion engine generator (G1, G2).