Not only do you need 19.5 volts to boot the laptop you require the correct amperage too lower amperage will cause the power lead to fail as the laptop will be drawing more. Also depending on the power your laptop requires correct wattage should be supplied to it? So the correct power lead is often the case. Sometimes you can get lucky and find a matching lead.
I have two 19.5 volt leads that supply two different laptops but i can't find one of the leads at the moment and i know I can't use the existing lead in the other as it would draw too much power and causing the brick (Power Supply) to fail. The amperage rating is higher in the missing lead.
Also polarity has to be correct on the laptop plug. Polarity being positive and negative wiring..