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.