Wake-induced vibration (WIV) is a special case of vortex induced vibration, which occurs in tandem cylinders. The downstream cylinder moving across the wake from the upstream cylinder oscillates under the alternating lift force. In a previous study by the authors, the downstream cylinder was pivoted to the upstream cylinder, thereby developing a swinging motion, which was termed as the pendulum system of tandem cylinders (PSTC). They found that the PSTC exhibits higher energy conversion efficiency than the conventional translational system of tandem cylinders (TSTC). In this study, the changes in the WIV characteristics were investigated experimentally with varying geometry conditions, such as the shape of the upstream cylinder and the spacing between two cylinders. Nine cases were tested by combining three upstream cylinder shapes (i.e., circle, square, and diamond) and three cylinder spacing values (S/D = 3, 4, 5). For each case, the reduced velocity (U* = V/Df0) was varied in the 0 ≤ U* ≤ 50 range. In addition to the mechanical response measurement of the downstream cylinder, the electrical power generated by the swinging motion was also measured. Results show that the maximum response was obtained for the circular upstream cylinder and S/D = 3, which is inconsistent with that obtained in the previous study.