Does A Usb Wifi Ac Adapter Bypass Internal Nic Card?

I've got an older laptop with an internal Ethernet 10/100 NIC card and a 2.4g wireless adapter.
I now have an ISP Internet package that provides up to 250mb download speeds. However I can never get over 100mb as it seems both my internal wired and wireless max out at 100mb.

If I purchase a usb wireless ac adapter that can handle download speeds of 300mb @ 2.4g and & 800+mb @5g will:
1) I get the speeds I'm paying for (up to 250mb download) or
2) the fact my PC's internal NIC (network interface card) max is 100mb that's all I can expect?

In other words, does a usb wireless ac dual band adapter work independent of all other network devices on one's PC to provide the best Internet speed or is the speed still throttled by one's PC internal NIC card limitations.

 

USB wifi adapter does not depend on slow/fast/non-working internal NIC.
Just be sure you read the reviews because all ac wifi adapters are not equal.
Here's a recent review
http://www.techhive.com/article/209...802-11ac-wi-fi-usb-adapters-to-the-limit.html

 

Thanks plodr for the explanation and review link!