You did not mention the form factor of your system. But generally there is a latch that must be pressed to release the PSU. You should see it at the back and bottom of the PSU next to the case and no Dell does not glue in the PSU.
 I have Optiplex 755... I am trying to get power supply out and replace, but it is either stuck or glued...  My computer won't turn on, so I am hoping it is power supply...Thanks for any help....
Needing to remove power supply