WP Super Cache is a plugin for WordPress that allows you to speed up your site by making use of server side caching. The plugin itself can be extended through the use of Super Cache plugins. Ideally you should move the Super Cache plugins folder from its default location (wp-content/plugins/wp-super-cache/plugins/) as otherwise whenever you upgrade the super cache plugin it will overwrite its plugins directory.
I suggest moving the folder to wp-content/wpsc-plugins/. You’ll then need to edit the wp-content/wp-cache-config.php file to change the location where WP Super Cache looks for the plugins. Find the line that says:
$wp_cache_plugins_dir = WPCACHEHOME . 'plugins';and change it to:
$wp_cache_plugins_dir = WP_CONTENT_DIR . '/wpsc-plugins';