One of the most challenging issues in today's high-performance VLSI design is to ensure high-quality power supply to each individual circuit blocks. Reduced power supply voltage can result in slower cell switching, or even circuit failure. Nevertheless, most floorplanning methodologies have ignored power supply considerations. Thus, the resulting floorplan may suffer from local hot spots and insufficient power supply for certain circuit blocks. In this paper, we present an optimal power supply planning algorithm based on network flow to shorten the current paths from power bumps to local power supply wirings. We have incorporated our algorithm into a floorplanning algorithm for integrated floorplanning and power supply planning. Experimental results are encouraging.