Laptop memory upgrade for Vostro 3550

I tried to upgrade my memmory on laptop Dell Vostro 3550,
compatibility issue puzzled me a bit I connected
with Dell support live chat, provide them ServiseTag and they offered me upgrade

http://accessories.us.dell.com/sna/productdetail.aspx?c=us&l=en&s=bsd&cs=04&sku=A5039677&baynote_bnrank=0&baynote_irrank=0&~ck=baynoteSearch

I searche the same .. but in twice lower in price

http://www.newegg.com/Product/Product.aspx?Item=N82E16820148492 but still not sure about compatibility

finally I go to http://www.crucial.com/index.aspx and it privided me compatible memory for my laptop. With 5% off cupon.

So bye memory is simple :)