Poly-3,4-ethylenedioxythiophene:polystyrene sulfonate (PEDOT:PSS) is a widely used conducting polymer with versatile applications in organic electronics. The addition of various salts during the preparation of PEDOT:PSS films can significantly influence their electrochemical properties. In this study, we systematically investigated the effects of different salt additives on the electrochemical properties, morphology, and structure of PEDOT:PSS films using a variety of experimental techniques, including cyclic voltammetry, electrochemical impedance spectroscopy, operando conductance measurements and in situ UV-VIS spectroelectrochemistry. Our results showed that the electrochemical properties of the films are closely related to the nature of the additives used and allowed us to establish a probable relationship with the Hofmeister series. The correlation coefficients obtained for the capacitance and Hofmeister series descriptors indicate a strong relationship between the salt additives and the electrochemical activity of PEDOT:PSS films. The work allows us to better understand the processes occurring within PEDOT:PSS films during modification with different salts. It also demonstrates the potential for fine-tuning the properties of PEDOT:PSS films by selecting appropriate salt additives. Our findings can contribute to the development of more efficient and tailored PEDOT:PSS-based devices for a wide range of applications, including supercapacitors, batteries, electrochemical transistors, and sensors.