Wireless charging is becoming an increasingly popular charging solution in portable electronic products for a more convenient and safer charging experience than conventional wired charging. However, our research identified new vulnerabilities in wireless charging systems, making them susceptible to intentional electromagnetic interference. These vulnerabilities facilitate a set of novel attack vectors, enabling adversaries to manipulate the charger and perform a series of attacks. In this paper, we propose VoltSchemer, a set of innovative attacks that grant attackers control over commercial-off-the-shelf wireless chargers merely by modulating the voltage from the power supply. These attacks represent the first of its kind, exploiting voltage noises from the power supply to manipulate wireless chargers without necessitating any malicious modifications to the chargers themselves. The significant threats imposed by VoltSchemer are substantiated by three practical attacks, where a charger can be manipulated to: control voice assistants via inaudible voice commands, damage devices being charged through overcharging or overheating, and bypass Qi-standard specified foreign-object-detection mechanism to damage valuable items exposed to intense magnetic fields. We demonstrate the effectiveness and practicality of the VoltSchemer attacks with successful attacks on 9 top-selling COTS wireless chargers. Furthermore, we discuss the security implications of our findings and suggest possible countermeasures to mitigate potential threats.