A power supply device and method for selection of a supply voltage or current to be applied to a lighting system having light-emitting diodes. A processing circuit performs automatic detection of the direction of connection of the lighting system by injecting at least one polarity test current pulse. Monitoring of the supply voltage and current during the polarity test current pulse, and reversal of the direction of the current or voltage for monitoring the direction of current flow for attribution of the direction of the supply voltage or current, are also performed. The device and method also include detection of the type of lighting system to be supplied with regulated voltage or regulated current according to the dynamic resistance of said system.