If the newer laptop draws a current which requires a 90 Watt charger, it might overload the lower rated charger and ultimately burn it out. If the older laptop only requires 65 Watts, that's all the power it will draw, even with a 90 Watt charger connected.
"And presumably you mean the output voltage?"
Yes, the tip that plugs into the laptop must have the correct voltage and polarity.
This thread is now locked and can not be replied to.