This is not a supported feature of PowerStore 3 but if you alter the products query slightly you can get it to display the category of the first item in the recordset by making these changes.
1) on line 84 of Products_Results.php update the code from this:
$WADbSearch1->whereClause .= "ProductID
to this
$WADbSearch1->whereClause .= "ps3_products.ProductID
2) on line 136 update the query to look like this:
$query_WADAProducts = "SELECT * , coalesce((select ps3_productoptions.GroupingID from ps3_productoptions WHERE ps3_productoptions.ProductID = ps3_products.ProductID limit 1),ps3_products.ProductID) AS GroupingID FROM ps3_products JOIN ps3_productcategories ON ps3_products.ProductID = ps3_productcategories.ProductID JOIN ps3_categories ON ps3_productcategories.CategoryID = ps3_categories.CategoryID WHERE ProductLive = 1 GROUP BY GroupingID ORDER BY ProductName";
3) you can then display the category name with this php code near line 426
<?php echo $row_WADAProducts["CategoryName"]; ?>
Keep in mind though that this will only display the category for the first item in the recordset, and this will only display if there are items returned from the recordset. So if you do a search for a particular category it will work just fine, but if you view the results without any filtering then then you will see the category for the first item in the list.
It might be a better idea to make these changes then display the category name inside of the item display next to it's name.