Modular DC/DC electrical-energy conversion system with a plurality of modules, intended to convert electrical energy supplied by an electrical-energy supply source delivering a first differential DC input voltage and a first DC input current, into electrical energy delivered as an output from at least two different rectifying conversion modules, the conversion system comprising a first supply terminal and a second supply terminal, configured so as to be connected to the supply source and to receive respectively a first supply voltage Vc1 and a second supply voltage Vc2, both DC, the first supply voltage Vc1 being higher than the second supply voltage Vc2, a single-phase primary converter having an asymmetric bridge structure controlled for fixed or regulated duty factor, comprising a first bridge arm and a second bridge arm, each connected between the first and second supply terminals (6, 8), the first bridge arm being formed by a first electronic switch controlled by a first control means, and a first freewheeling and demagnetisation diode, the first freewheeling diode being connected in series to the first electronic switch in a first intermediate terminal and to the second supply terminal, the second bridge arm being formed by a second electronic switch controlled by a second control means, and a second freewheeling and demagnetisation diode, the second freewheeling diode being connected to the second electronic switch in a second intermediate terminal and to the first supply terminal, the first and second control means (26, 33) being configured so as to control, by pulses repeated periodically, in conduction and at the same time, the first switch and the second switch, the voltage Ve1 delivered to the first intermediate terminal being higher than the voltage Ve2 delivered to the second intermediate terminal when the first and second switches (24, 32) are in simultaneous conduction, at least two rectifying conversion modules (12, 14; 412, 14; 612, 614; 712, 714; 1022, 1024), connected as an input between the first and second intermediate terminals (30, 36) of the single-phase primary converter, each of the at least two conversion modules (12, 14; 612, 614; 1022, 1024) comprising a different transformer (40, 42; 1012, 1014) having a single primary winding (50, 52; 1050, 1052) connected between the first and second intermediate terminals (30, 36) of the single-phase primary converter, and at least one useful-load secondary winding (56, 58; 1056, 1058), and associated uniquely with each secondary winding (56, 58; 1056, 1058), a different single-phase rectifier (66, 68; 1066, 1068), a cell for filtering different residual ripples (76, 78; 1076, 1078), a separate pair (86, 88; 1086, 1088) of modular end output terminals, the transformer (40, 42; 1012, 1014), the single-phase rectifier (50, 52; 1050, 1052) and the filtering cell (76, 78; 1076, 1078) being configured so as to convert the electrical energy supplied as an output from the single-phase primary converter into electrical energy delivered to the pair of modular end output terminals, at a predetermined modular differential output voltage for a predetermined modular output load current, characterised in that each different and unique primary winding (50, 52; 1050, 1052), associated with a different conversion module (12, 14; 1022, 1024), comprises a first primary-winding terminal (150, 160; 1252, 1256) and a second primary-winding terminal (152, 162; 1254, 1258), electrically connected respectively to the first intermediate terminal and to the second intermediate terminal of the primary converter, and among the total number N of conversion modules supplied by the primary converter, each of at least the total number N minus one of the conversion modules (14; 1024) comprises respectively a first magnetisation isolation diode (182; 1182) connected directly or through a wire connection in series with the associated primary winding (52; 1052) at one of its first and second terminals (160, 162; 1056, 1058) in order to form a series circuit connected between the first intermediate terminal and the second intermediate terminal, and biased in the direction of conduction towards the second intermediate terminal, and a second demagnetisation isolation diode (192; 1192) connected either to the primary winding of the associated transformer or to a secondary winding of the associated transformer taken from the at least one useful-load winding or a supplementary secondary winding dedicated solely to demagnetisation.