I have a laptop with 19.5v, the original adapter blew up and i managed to get a universal adapter. The problem is the Uni adapter has 19v,20 and so on but not 19.5, so is it possible to use it at 20v? will there be any damage to the laptop?
The PC power supplies have a tolerance of +/- 5 % on all voltages, such as 12 VDC, 5 VDC and 3.3 VDC.
If we assume, just assume, that the same applies to notebook power supplies, then 19.5 VDC has a lower limit of 18.5 VDC and an upper limit of 20.5 VDC, then no harm should be done to your notebook using a 20 VDC power supply.
Personally, I would use it straight. At the worst situation, it may slightly decrease battery life but it will not cause a fire as long as your power supply is not defective.
If you are not comfortable with 20 VDC, set it to 19 VDC. You will still have satisfactory charging of the battery and continuous power feed to your notebook.
The important thing is that the amperage of your new power supply should not be less than the amperage needed by your notebook.