Laptop Adapter current request
You can measure current with a multimeter in series (i.e. you have to break the circuit somewhere and put the multimeter in the circuit).  However, how are you going to measure the current draw without the correct rated PSU?  If it requires somewhere between 3.25A and 4.5A, you will not get a true representation of its requirement.
Yes, you can damage the charger and quite possibly the laptop.  I am a laptop engineer and have seen a lot of damage due to incorrect PSU usage.  The PSU can overheat, which is a fire risk.  This can in turn melt the socket on the laptop, or cause further damage.


Always use a PSU that is rated correctly.  If your laptop came with a 90W PSU, don't use a 65W PSU.  You'll find replacement PSUs on eBay are very cheap (try searching brand model PSU, e.g. "Acer 5200 PSU", or you can get a universal laptop PSU from many computer retailers - especially the ones that sell spare parts.