This paper mainly analyses a linear circuit with two power sources. There are three types of this circuit: the current - controlled dual - port network，voltage - controlled dual - port network and hybrid dual - port network. A dual-port network VCR can be obtained by measuring and other methods. The physical distribution of each part of the power of two power sources can be obtained when the VCR of two-port network is known. The power of each power supply consists of two parts. One part is equal to the power provided by the power supply when it is connected to the circuit separately. Another part is the increased power due to the interaction between the two power sources when they are both connected to the circuit. The increased power depends on two power sources and circuit parameters. According to the reciprocity theorem，when there is no controlled source，for current-controlled twoport networks and voltage-controlled two-port networks，the increased power of each power source due to interaction

is equal. That is to say，the increased loss power of the circuit is shared equally by the two power sources. For a hybrid dual-port network，when there is no controlled source，the increased absorption power of one power source is equal to the increased supply power of another power source due to the interaction. The sum of the power of both power supplies is equal to the sum of the power of both power supplies when it is connected to the circuit separately. In this case，the effect of interaction is that one power source charges another power source. The results of this study are universal. It can help one to solve the power source problem of power grid，and can also solve the power source problem of other electronic circuits.