It's not defective;  it is a 10/100 adapter.  Specifications here: [URL]  
Hi, I have an Inspiron 5558 labtop. according to its servicetag it is equipped with a Realtek chip, that seems to be a gigabit card. My problem is, every time I connect the lan to a GB-Lan, the control panel remarks a 100 MB connection. I've installed the apropriate drivers under win 10, the card is set to auto-negotiation (speed&duplex). Is the controller defective?? maybe I havn't set all params right... hopefully someone may help me out Tia Mike  
Dell 5558 ethernet card connection speed