A merchandise security system for electrical appliances, comprising - a security center comprising a plurality of terminals , - at least one power unit attached via a first connection to one of the terminals , - and at least one security head for affixing to an appliance to be secured, which is attached via a second connection to the power unit , wherein the security head has a security sensor for producing a sensor signal in the event of the security head being separated from the appliance , characterized in that the security center is configured to trigger an alarm when the sensor signal is detected, - wherein the security center is configured to provide electric power for the power unit with a fixed current or fixed voltage via the first connection , - and the power unit has an adjustable electric converter in order to convert the electric power provided via the first connection into a supply current or a supply voltage, which is supplied via the second connection to a supply terminal on the security head , - wherein the security head and the power unit are configured such that an adjustment signal for the electric converter is transmitted via the second connection, - and the electric converter is adjusted according to the adjustment signal, - wherein a measuring device for determining a measured value of the voltage and/or of the current at the supply terminal is provided on the security head , - and wherein the power unit and the security head are configured such that a deviation is determined between the measured value and a default value, - and the electric converter is regulated in accordance with the deviation. - a security center comprising a plurality of terminals , - at least one power unit attached via a first connection to one of the terminals , - and at least one security head for affixing to an appliance to be secured, which is attached via a second connection to the power unit , wherein the security head has a security sensor for producing a sensor signal in the event of the security head being separated from the appliance , characterized in that the security center is configured to trigger an alarm when the sensor signal is detected, - wherein the security center is configured to provide electric power for the power unit with a fixed current or fixed voltage via the first connection , - and the power unit has an adjustable electric converter in order to convert the electric power provided via the first connection into a supply current or a supply voltage, which is supplied via the second connection to a supply terminal on the security head , - wherein the security head and the power unit are configured such that an adjustment signal for the electric converter is transmitted via the second connection, - and the electric converter is adjusted according to the adjustment signal, - wherein a measuring device for determining a measured value of the voltage and/or of the current at the supply terminal is provided on the security head , - and wherein the power unit and the security head are configured such that a deviation is determined between the measured value and a default value, - and the electric converter is regulated in accordance with the deviation. <EOS>