How come the input drawing current be constant (1.5A) even though it shows that the adapter is universal input (100-240V)? I mean that the power supply voltage varies in different locations still how come the current be same.
The input current is not constant. The 1.5 A figure refers to the worst case, meaning the value that is guaranteed not to be exceeded under all combinations of valid conditions.
In this case, the combination of conditions is probably with 100 V in and 4.62 A out, although that is not explicitly stated, so you shouldn't rely on that.
The marking gives you the maximum current, not the typical current. As others have said that will generally occur at minimum input voltage and maximum output current (and maximum ambient temperature, where losses are greatest). Typically input current will be minimum under the opposite conditions, and some adapters may have an extra-low-power mode for when the load side is unplugged.
If you are interested in the power consumed rather than current (the input will likely not have power factor correction (PFC)) then refer to the efficiency rating V which indicates a minimum efficiency of 87%, so at full output current it should draw less than 103W.