Typically when a plugin jar file is placed in your Capital plugins folder, you would expect that the plugin would appear when you go to "Capital > System > Plugins" in the ribbon menu. There are some cases where plugins may fail to load due to errors in the configuration of coding of the plugin. In most cases an error will be reported in the output window if a plugin fails to load.
Check your Capital log files for any plugin errors and resolve the errors.
There is one case where plugins may fail to load but no error is reported. This can occur if you name a package name in conflict with Capital's existing class paths.
For instance: The capitalapi.jar file contains a class path "com.mentor.chs.plugin.drc" where various classes are located for plugin DRCs.
If you create a plugin DRC and set the package name where the plugin is located to "com.mentor.chs.plugin.drc", the plugin will not be loaded and no error is reported.