I have got some DC Power Supplys for some projects one 6 volt and one 5 volt the 5 volt one reads 5.5volts but the 6 volt one reads 8.1 volts the circuit board that it is powering says 5 to 7.5 volts will it be ok with it and also i tested some more power supplys and some read close to the output voltage and others where way off like a 12 volt one said
18 volts why is this? cheers