When testing a laptop power connector, the voltage measured has be close to +/- 5% to the accepted voltage of the laptop. This is to ensure that the power connector would not pose any hazard to the user and is safe for use. So, for instance the accepted voltage is 19 V, when you test the power connector it should be that the reading is between 18 V to 20 V. Any reading below or above that range is not recommended for use. You can locate the accepted voltage on the battery or the laptop itself. To test a power connector, you can use a volt meter or a multi meter.