diff -u b/core/modules/system/system.module b/core/modules/system/system.module
--- b/core/modules/system/system.module
+++ b/core/modules/system/system.module
@@ -136,6 +136,12 @@
       }
       break;
 
+    case 'block.admin_add':
+      if ($request->attributes->get('plugin_id') == 'system_powered_by_block') {
+        return '<p>' . t('The <em>Powered by Drupal</em> block is an optional link to the home page of the Drupal project. While there is absolutely no requirement that sites feature this link, it may be used to show support for Drupal.') . '</p>';
+      }
+      break;
+
     case 'system.site_maintenance_mode':
       if (\Drupal::currentUser()->id() == 1) {
         return '<p>' . t('Use maintenance mode when making major updates, particularly if the updates could disrupt visitors or the update process. Examples include upgrading, importing or exporting content, modifying a theme, modifying content types, and making backups.') . '</p>';