why the speed get reduced to near half on usb to ethernet connection

Hi, Ofcourse, I know that ethernet connection gets you the maximum speed that your ISP allots to you than wifi.
But , When I use usb to ethernet, my lan port damaged, connection, the speed is nearly half of the speed what I will get in from direct ethernet port.
Is there any technical reasons for this
I could just see that the signal from usb port , modifies to ethernet port and then passed on to the modem.
Could some one clearly say, why this happens and how could fix.
thanks.

I use a Realtek RTL8153 USB3 gigabit adapter in computers that have an integrated ethernet device that doesn't support gigabit speeds or doesn't work.
After I install the software driver package for it and then go into its properties window and configure its settings, it works fine and provides full download and upload speeds.
We're not there to see what you have and what you're doing, but it's my guess you're doing something wrong.

Hi, Flavelle, I mentioned usb 2.0 ports to ethernet adapter.
Please let me know the settings you talk in the adapter device. I will try
There are usual tabs like general , advanced, driver and details.
which is to be tweaked to get the full speed , please

- - - Updated - - -

Hi, Flavelle, I am expecting your tips on the tweaks in adapter settings