Electrical outlet on a dimmer switch?
Outlets are not supposed to be dimmed!

While this might seem like a good idea if you wanted to plug in a table lamp that lacked its own dimmer, it creates a dangerous situation since outlets can accommodate any device with a plug, and some devices, such as many motors, react very badly to the output of a dimmer. It is forbidden under 404.14(E): 


  General use dimmer switches shall be used only to control permanently installed incandescent luminaires unless listed for the control of other loads and installed accordingly.


The other load dimmers are for fluorescent, LED or CLF fixtures. Dimmers are not listed for standard outlets.

The first thing I would do is replace the dimmer with a standard switch. (Done with power from the breaker turned off.) I would also check the outlet to see if it appears to be wired correctly -- black wire to brass, white wire to silver, green/bare to ground. Restore power and check the outlet again. 

Supplement
Also see the answer by @ThreePhaseEel that explains specialized outlets that can be dimmed, and the associated code.