A power system capable of detecting a foreign object includes a power supplier side, a power receiver side and a cable. The power supplier side includes a power control switch, a power control circuit and a pull-up circuit. The power control circuit controls the power control switch to provide a supply voltage to the power receiver side. The pull-up circuit provides a supplier transmission current to generate a supplier transmission voltage for determining whether the power supplier side and the power receiver side are coupled properly. The power control circuit determines whether a foreign object exists between the power supplier side and the power receiver side according to a voltage difference of the supplier transmission voltage before and after the supply voltage VBUS is provided. The power control circuit adaptively controls the power control switch and adjusts the transmission current according to whether a foreign object exists.