I have both the ACP-12U and ACP-7U. Although the marked output voltage on the ACP-12U is 5.7V, it is measued by a multimeter to be 6.02V. The ACP-7U is marked as 3.7V, but measued to be 9.9V. I also has a UBS cable charge for Nokia, it is measured to be 8.2V.
All of them works when I plug them to my Nokia 6230i phone, I am not sure why there are such hugh difference between then marked voltage and the real measured voltage. Anyone ther knows more about chargere can explain the reason?
Because it is open circuit voltage. Voltage for these chargers are regulated only under load. You should add load and then measure the voltage. For these "dumb" chargers the voltage may fluctate depending of the load. The specification says for example 5.7V 500mA, It means the voltage is 5.7V when load is 500mA if load is lower/higher the voltage will measure different.