What are the full specs on your machine? The 4670 has a TDP of ~60W, if you are running a low power dual core you might be alright, but since you can get an EA-380D for only $30 after MIR it seems silly to risk it. The EA-380 will easily power a 4670, but if you want the option of a more powerful card in the future definitely consider a good 550.
http://www.newegg.com/Product/Product.aspx?Item=N82E16817371033