AC Adapter

Hello, I have an iMac mid-2011 model 27". It works with b/g/n protocol and I want to upgrade it. I've found an AC Adapter (dual band-1900 Mbps) but wondering if I will see any difference in my network.
Also I have an IPTV device which can connects to 2.4 GHz. If I hook up this adapter I'll be able to connect at 5GHz ?

 

I'm interested to improve my Wi-Fi. I don't mind so much for Internet.
Thinking to buy one dual band adapter for IPTV and one AC dual band for iMac.
Please advice me.