There are some speakers that can connect to your computer and power up via a usb. In term, these speakers also include an integrated headphone (audio jack) jack on the side of the speaker itself.
This is strange though....What kind of computer doesn't have audio jacks
Also, I have an xps 8000. I found that the head phone jacks are actually in a hidden compartment. Is your desktop black? There should be a sliding plastic black (or whatever color) door that you can lift up and find hidden several usb ports and audio jacks.