Hi Michael,
Canon 550D have use one usb shape connector for two tasks:
– USB —> upper part of the connector, 5 pins
– AV out —> lower part of the connector, 6 pins
Any mini USB cable will work with the Canon 550D for USB task but there is no way that the same cable will allow AV out .

On Ebay you can buy in China a non original cable for 10 USD , look at item 260723669452