Cache Time is a simple, but yet advanced plugin that displays the time that the current page was cached.
Cache Time is meant to display the time that your website last cached the current page, for both you and your users benefit. There are many instances where users want the most current information, and this is an easy way to show how current that info is.
Officially, yes. WP-Super-Cache may work, though I have not tested it.
If no caching system is installed, the plugin simply displays the current time.