Can you try by this way, I think this will solve your problem

    $collection->addFieldToFilter(array(
              array('attribute' => 'supplier_id', 'like' => '1'),
              array('attribute' => 'product_type', 'like' => 'first_type')
    ));
    $collection->addFieldToFilter(array(
              array('attribute' => 'supplier_id', 'like' => '2'),
              array('attribute' => 'product_type', 'like' => 'another_type')
    ));