I have a recording studio but all my audio production is done with an external USB connected unit (MOTU 4Pre) and not the internal PC audio. For testing, connect the headset to the rear speaker (Green) jack and see if it has the same problems. Many Dells use Waves MaxxAudio in conjunction with Realtek audio. MaxxAudio is used for jack detection (what type of device). Check your MaxxAudio for proper headphone detection and for any added effects such as reverb or delay.  Maybe even reinstall the Dell 7080 model specific sound driver (that also reinstalls MaxxAudio).   In the future always include the version of 7080 on any initial problem post.  e.g. Small Form Factor (SFF),  Tower, etc.    
When I plug in my headphones to my PC, there is an unintended reverb and echo in the sound.  I do not have this issue while using the same headphones with my dell laptop, it is just with this computer. I know nothing is wrong with the headphones.  This is a problem as I am involved in music production and find this effect very annoying as it distorts/alters the sound.  How can I fix this issue?  Thank you
Optiplex 7080 - Echo/reverb when using headphones