Can you try by this way, I think this will solve your problem
->getSelect()->where(" (`Your attribute` = 'Value' AND `Your attribute` = 'Value') OR (`Your attribute` = 'Value' AND `Your attribute` = 'Value')");
In your case in the getSelect() could be:
->getSelect()->where("(`supplier_id` = '1' AND `product_type` = 'first_type') OR (`supplier_id` = '2' AND `product_type` = 'another_type')");