Is it possible to use a laptop charger in other laptop with different specifications? [duplicate]

Possible Duplicate:
Charging laptop with non-original charger
Can a 20V 4.51A power supply be used with a computer that requires a 19V 3.42A power supply?

Let's say I have my laptop charger that uses 19.5V and 3.9A and I want to use it in other laptop that has no charger but it needs just 19V and 3.16A, I've studied a little of electtronics and I know that the amperage doesn't affect because the computer will use just the necessary, but I'm not really sure about the voltage.

I read this post and I know the polarity is the same and the connector fits, but it doesn't say anything about voltage, I also know if the voltage of the charger were lower than the specification it'll not be a problem, but what about this little almost insignificant difference??

Many modern laptop power supplies are not only provide the DC to the laptop over the cord but also have a third, signal wire in the cord.

This signal wire is used by the schematic/software to detect the type of the AC/DC adapter and possibly control the adapter itself. For example, to reduce its power consumption when the battery is charged completely.

So, theoretically you can use this power supply with your notebook but do not expect that everything will be fine.

I have a Dell notebook that had its power supply cord torn several times. I was soldering it each time, but eventually it was getting broken again. When this third signal wire was torn then the battery charging were impossible while I was able to switch the notebook on.

And remember please, if you do it - you do it at your own risk