The listing, Dell Laptop Adapter, round-pin style has ended.
Dell 90w AC adapter, Model NADP-90KB A, part number C2894. I just tested the output and it's 19.49 volts direct current. The outside diameter of the pin that goes into the laptop is a little over 1/4 inch, as second picture shows. Inside, there is a male "wire-pin" that I tried to illustrate in the third picture. Free shipping to U.S. Will consider free shipping to Canada if bid goes over 10,000 points.