Dell 8700 USB gigabit Ethernet Adapter

A USB Ethernet adapter isn't the same thing as the onboard NIC.

If you have a USB network adapter, unplug it from USB and connect your Ethernet cable directly into the onboard Ethernet port on rear of PC. Then configure your network settings in Windows.

Hi, thanks for the response. I might have been unclear. I am currently running 100baset from the existing chassis based ethernet port. If I look at the device manager it says there is a usb gigabit Ethernet adapter. I am trying to find where to connect to this adapter since I never bought one. In the network section of Windows it also says I have a gigabit adapter with wire unplugged. So obviously the gigabit hardware is there somewhere or the drivers would not have loaded.

I am confused.

"I am currently running 100BaseT from the existing chassis based Ethernet port."

So you are connecting like this?
Router RJ-45 out port --> Ethernet cable --> XPS 8700 NIC RJ-45 in port

"If I look at the device manager it says there is a USB gigabit Ethernet adapter."
Did you at some point plug in an external USB Gigabyte Ethernet adapter into a USB port on the XPS 8700?

"I am trying to find where to connect to this adapter since I never bought one."
You lost me on that. Are you saying you have not yet bought one and want to know where it would in theory plug in? Or are you saying you bought one and plugged it in?

Why use an external USB Gigabyte Ethernet adapter when the onboard RJ-45 is capable of 10/100/1000 Mbps?

You're definitely being unclear and I'm as confused as Dell-Chris is...

Let me ask different questions:

If your Ethernet connection is working, why do you care what Device Manager says?

Presumably PC is hardwired to the router, so what speed are you getting to the router?

Are router and modem capable of gigabit speed?

What is max speed your ISP is providing to you?

Yes, I am hard wired from the router RJ-45 through cat5 to the RJ-45 on the back of the 8700. No I didn't purchase a gigabit Ethernet to usb  dongle so none have been plugged into any external USB slot. Yet in the network screen there is a gigabit Ethernet device that says cable unplugged. The Realtek shows connected and active. In device manager it also shows the usb gigabit Ethernet as installed and driver loaded.

Weird!

Manually set a System Restore point, to be safe. Then open Device Manager and right-click that  USB gigabit Ethernet adaptor and Uninstall it. Exit Device Manager and reboot.

Is everything still working correctly now? And check in Device Manager to make sure that pesky USB entry is gone and no "Unknown Device" entries show up.

Yeah, I already tried that and the gig usb entry comes back! The other thing is I can't get 1000baseT out of the Nic. This was a win upgrade from  win 8.x so all bets are off as to what's going on.

Have you scanned thoroughly for malware recently?

What USB devices are connected to this PC? Does your monitor have USB ports and a USB connection to the PC? Does your printer have an Ethernet port? What happens if you disconnect all USB devices, except mouse and keyboard? Does that USB Ethernet device disappear?

How do you know you're not getting gigabit speed? Does the NIC have LEDs next to the jack on the back of the  PC? I don't know what color LED would indicate a gigabit connection from your Realtek NIC to the router, but maybe Chris can find out and post that info for you.

Are your router and modem capable of gigabit connections?  

Do you have gigabit service from your ISP? Just because the NIC, router, and modem may be capable of gigabit speeds, that doesn't mean you get that between the modem and your ISP, unless you pay extra for it. So what speed is your ISP providing? Besides, speed is dependent on internet traffic too so you may never get their claimed speed.  Have you checked your speed at  a site like:  www.megapath.com/.../   ?

Is it time to wipe the hard drive and do a clean installation of Win 10 Fall Update?  Be sure to back up personal files on external media before doing a clean reinstall.