First of all, the nominal voltage of the general power supply refers to the voltage of the open circuit output, that is, the voltage when no external load is connected and there is no current output, so it can be understood that this voltage is the upper limit of the power supply output voltage.
In the case where an active voltage regulator is used inside the power supply, even if the mains voltage fluctuates, its output is a constant value, like a small transformer on the market, such as a power supply with a Walkman, if the mains fluctuates, The output of this power supply will also fluctuate accordingly.
Generally speaking, the true no-load voltage of a common power adapter is not necessarily the same as the nominal voltage. Because the characteristics of electronic components cannot be completely consistent, there is a certain error. The smaller the error, the higher the consistency requirement for electronic components. The cost of production is high, so the price is more expensive.
In addition, regarding the nominal current value, no matter any power source has a certain internal resistance, when the power supply output current, there will be a pressure drop inside, resulting in two things, one is to generate heat, so the power supply will be hot, and the other One is to cause the output voltage to drop, which is equivalent to internal consumption.