Simultaneous wireless information and power transfer (SWIPT) is an appealing solution to balance the energy distribution in wireless networks and improve the energy-efficiency of the entire network. In this paper, we study the optimal policies for SWIPT over the flat-fading channel subject to the co-channel interference. The SWIPT receiver using dynamic power splitting (DPS) is expected to achieve the maximum information rate given an average harvested energy constraint. In the case that channel state information at the transmitter (CSIT) is not available, the optimal power splitting is derived. For the case with CSIT, the joint optimal policy of the transmit power and the power splitting are also provided. Through simulations, we show the optimal rate-energy (R-E) trade-offs of our proposed policies. The case with CSIT achieves better R-E trade-off than the case with no CSIT.