A method for performing system power control within an electronic device and an associated apparatus are provided. The method includes the steps of: utilizing a power consumption index generator positioned in a specific subsystem to generate a power consumption index corresponding to the specific subsystem, where the electronic device includes a plurality of subsystems, and the specific subsystem is one of the plurality of subsystems; and triggering a power limiter protection operation for the electronic device according to the power consumption index. For example, the power consumption index corresponding to the specific subsystem may represent a power consumption value of the specific subsystem, and the method may further include: comparing the power consumption value of the specific subsystem with a peak power threshold to determine whether the power consumed by the specific subsystem reaches the peak power threshold to generate a determining result, for triggering the power limiter protection operation.