add_filter( 'the_title', 'custom_product_title', 10, 2 );
function custom_product_title( $title, $post_id ){
$post_type = get_post_field( 'post_type', $post_id, true );
if( in_array( $post_type, array( 'product', 'product_variation') ) ) {
$title = str_replace( '|', '<br/>', $title ); // we replace "|" by "<br>"
}
return $title;
}