Provided is an apparatus and method that may stably perform wireless transmission. According to one general aspect, a power supply for a wireless power transmitter may include: a detecting unit configured to detect voltage, current, or both supplied to a power amplifier (PA); a controller configured to determine power supplied to the PA based on the detected voltage, the detected current, or both, and to determine a reference current based on the determined power supplied to the PA; and a breaker configured to cut off the power supplied to the PA based on a comparison of current supplied to the PA and the reference current.