Charging System and Charging Method of Universal Serial Bus

A charging system includes a primary power source, a power source controller coupled to the primary power source, a first switch, a third switch, and a first port. The power source controller includes an auxiliary power source, a first auxiliary power terminal coupled to the auxiliary power source for providing a first detection current, and a load detection circuit. The power source controller initially sets the first switch to be off, the third switch to be on, and the first auxiliary power terminal to provide the first detection current to the first port through the third switch. When the first detection current is less than a threshold value, the power source controller maintains the first switch to be off, the third switch to be on, and the first auxiliary power terminal to provide the first detection current through the third switch.