I recently purchased a refurbished computer that does not have a sound card. I do not want to add an internal card, because it will void my warranty, unless I pay someone to install the card, which I would rather avoid. I found an external card, which looks like a network adapter and plugs into a USB outlet. Given that I have almost no sound, is this a good option? I have seen them for as little as $4. Thanks in advance...

Also, how does Class B amplification compare to the amplification of a standard internal sound card like SoundBlaster, etc.?...thanks again

The cards work just fine. And the sound is of good quality!