what do i need to know about laptop charger before buying it?

-> my laptop is dell inspiron i5 5567 laptop.

-> my charger specifications are 19.5V,3.34A,65W.

It is positive polarity adapter.

-> How do I know if it is small pin or large pin? (I am ordering online so need to know it) It seems like it is 4.5 mm.

-> The service tag is 8BNWK22