Serial Cable Converter RS232 to 3.5mm audio Jack Manufacturers tell you that the power supply is actually a "comprehensive transformer" composed of a transformer, an AC/DC converter, and a corresponding voltage regulator circuit.

Serial Cable Converter RS232 to 3.5mm audio Jack Manufacturers tell you that this "Comprehensive Transformer" contains two main components - "transformer" and "current converter", and these two components themselves have power consumption, they The attached voltage regulator circuit is no exception, so the power supply itself is a "consumer".
Serial Cable Converter RS232 to 3.5mm audio Jack Manufacturers tell you that the energy of the input power supply of the converter cannot be 100% converted into effective energy for the various components in the host, so there is a problem with conversion efficiency. Power conversion efficiency = instant output power provided by the power supply to the host / instant power of the input power supply × 100%.
The above is the Serial Cable Converter RS232 to 3.5mm audio Jack manufacturer's introduction and analysis of the working principle of the converter, hope it helps you.