voltage - Reading and understanding electrical specs on laptop AC adapters

My Dell laptop comes with an AC adapter with the following specs:

65 W
Input AC: 100 - 240 V, ~1.5 A, 50 - 60 Hz
Output DC: 19.5 V,  3.34 A

My HP laptop:

65 W
Input AC: 100 - 240 V, ~1.7 A, 50 - 60 Hz
Output DC: 18.5 V,  3.5 A

I have 3 questions:

1. 
   

   On the Input AC, why 1.5 A vs 1.7 A? I just have one type of power outlet for everything, such as lamp, TV, refrigerator, etc. So this number is not too significant?

   
   


2. 
   
   

   The output DC voltage and current are different. Would it be safe for me to interchange the adapters, i.e. use the HP laptop with the Dell AC adapter and vice versa. Which way would be safe and which is not?

   
   


3. 
   

   If there's another adapter with the same output DC but higher wattage, would I be able to use it as well?