There have been at least two artists performing under the name "Cosmo Topper"; 1) A current alternative rock band led by writer/composer/performer Morley Bartnoff; 2) A blues-rock band from Phoenix, popular during the 1970s and 1980s.
These are photos from concerts where Cosmo Topper played, so they may be of other bands that played the concert as well.
Powerslide
Powerslide / Lannie Flowers / Cosmo Topper / The Russ Tolman Band / Nelson Bragg / BUS Jul 31, 2013 Los Angeles, California, United States Uploaded by Wicked Goddess Credit: © Kathy Flynn/Wicked Goddess Photography