Pro singer goes to karaoke bar in disguise
Filed under stuff that pops up on YouTube:

Professional singer Jewel, disguised as a mild mannered businesswoman, drops by a local karaoke bar and performs some of her classic songs to a completely dumbfounded audience.

Some in the audience can not believe their own ears, hearing the voice coming out of the completely unknown woman in front of them, who sounds like a pro and actually 'almost' identical to the original artist. But it could obviously not have been her by the looks of it.

However, after her performance as "Karen," Jewel comes back as herself to sing some more, and it's also revealed to the audience that they had been duped the first time.