Polymer-supported phospholipid bilayers (PLBs) are popular model systems for the study of transmembrane proteins under conditions close to cellular membrane environments. In this work, by combining the techniques of dissipative quartz crystal microbalance and atomic force microscopy, we investigate the deposition of vesicles on a hydrated cationic poly(diallyldimethylammonium chloride) (PDDA) layer as a function of phospholipid composition and sodium chloride concentration. The vesicles used consist of phospholipid mixtures with varying amounts of net negative charge. Uniform PLBs are formed by either increasing the negative charge density of the vesicles or decreasing sodium chloride concentration, suggesting that the electrostatic attraction between the vesicle and PDDA layer is the driving force for the formation of the PLBs. Our results indicate that the PLB formation is a fast adsorption-rupture process of the vesicles, without passing through a critical vesicle density. We further contend that the fluctuating PDDA support plays a central role for this process. This work provides a framework for understanding the key factors that influence the formation of PLBs.