A voltage regulator for a merchandise display security device provides an appropriate operating voltage through a power cable electrically connected between an alarm sensor and an item of merchandise. The voltage regulator utilizes a feedback signal from a power conversion chip and data from a microprocessor look-up table to adjust the input power to the merchandise. The look-up table stores appropriate operating voltage requirements for each power cable used for different types and brands of merchandise. The type and brand of merchandise is identified by the resistance of the power cable and the feedback signal is modified continuously to maintain power to the merchandise at an appropriate operating voltage.