I am trying to find a power cord for my laptop, but each one that I find has the output which is what my input is, so I am not sure how to find a power cord for it. I have a
Compaq Presario 900 US, my Input Rating is 18.5V DC 3.5A. The cords I find have an Output of 18.5V 3.5A, how do I find the right one?

Here 'ya go:
Compaq Presario 900 ac adapter - $31

ComputerLogin :: 90W AC Adapter for Emachine HP Compaq Laptop = $30

Power Cord Charger Compaq Presario 900 900LA 900US 901 - eBay - $27