A light source apparatus and a light source adjusting module are provided. The light source apparatus includes a power supply, a phase modulator, an electrical transformer, a light source adjusting module and a light-emitting device. The power supply provides a first AC voltage signal. The phase modulator receives the first AC voltage signal and adjusts a conducting phase of the first AC voltage signal to generate a modulated AC voltage signal. The electrical transformer transforms the modulated AC voltage signal to generate a second AC voltage signal. The light adjusting module generates a luminance adjusting signal according to a state of the second AC voltage signal. The light-emitting device receives the luminance adjusting signal to generate a corresponding light source.