Check the specifications of the power supply unit: Look on the hoover itself or in the operating instructions for the details of the charger (e.g. voltage, current and wattage). Typical specifications are e.g. 24V or 26V at 1A to 2A.
Buy an original power supply unit: Look for an original power supply unit to ensure that it works optimally with your device. You can often find spare parts on platforms such as Amazon, eBay, digitec, galaxus or the Xiaomi shop.
Universal charger: If you can't find an original power supply, you can also use a universal charger that has the same specifications as the original. Pay close attention to the correct values (e.g. voltage, plug size) and I would recommend looking for an original spare part for the Xiaomi G20 Lite to avoid compatibility problems.