A switching power supply and a power supply apparatus that incorporates the switching power supply are provided. Advantages of the switching power supply include the following: 1. Two or more switching power supplies can be used in parallel when they have the same kind of input power and the same rated output power. 2. Two or more switching power supplies can be used in parallel when they have the same rated output power but different kinds of input power. 3. Two or more switching power supplies can be used in parallel when they have the same kind of input power but different rated output powers. 4. Two or more switching power supplies can be used in parallel when they have different kinds of input power and different rated output power. 5. When the above-described switching power supplies are connected in parallel, the respective load proportion of each of them can be adjusted at will.