The object of the invention is to provide a power supply system and method for the various elements forming DC/AC electronic power converters that assures the operation of the converters during normal operating conditions and anomalous operating conditions, being specially designed for photovoltaic systems connected to the power grid and capable of providing direct current and alternating current voltages at the output thereof from at least one DC power source (1) and at least one AC power source (2), which basically comprises an output for DC loads (6) connected to the output of a DC/DC converter (3) the input of which is connected to the DC power source (1), an AC output for critical loads (7) connected to a first selector (5) configured for alternating between a first position where said AC output for critical loads (7) is connected to the output of a first DC/AC converter (4) the input of which is connected to the DC power source (1), and a second position where said AC output for critical loads (7) is connected to the AC power source (2), an AC output for non-critical loads (8) connected to the AC power source (2) and a control unit (9) controlling the operation of said first selector (5).