You need to pass the category name as well if you want to show posts from specific category..
You just need to add one more param to the get_posts array.
REPLACE THIS
<? $products = get_posts( array('post_type' => 'products', 'posts_per_page' => 400,) ); ?>
WIth THIS
<? $products = get_posts( array('post_type' => 'products', 'category_name' => 'category_name_here', 'posts_per_page' => 400,) ); ?>