Computer already have female audio jack used as audio output. I was shocked when I found devices like USB External sound card which we can insert it into USB port which is now acts as audio output. I always thought USB port only for data transfer and power transfer.
Pictured is a classic audio-class USB device. This is a digital audio device. It does have a high-quality D/A converter that converts digital data stream from USB channel into audio. It also usually has an input channel working in opposite direction, A/D converter into digital data stream, to support mike in a headset, or just a line input.
On a system level the initial state of drivers usually associates all audio streams with the on-board audio codec connected to back/front audio jacks. However, when a USB dongle of audio class is detected on a USB port, the system automatically re-assigns all audio streams (system sounds, music, video playback) to the USB dongle. When the dongle gets removed, the system redirects all sound back the default internal device.
It is a very convenient feature when main sound drivers are screwed: the USB audio drivers are fairly standard and robust, and the USB sound always works (in my experience), unlike various on-board proprietary audio codecs that frequently need special drivers that might be not always available or not supported any longer.