This is not "sour cream & onion" flavour. I can taste only 3 different flavours in chips. For me there are "salt and herbs" "vinegar" and "smoked salt w/ paprika".
Sour Cream and onion is the vinegar taste. It's oniony taste is from sulphur. Like when you mix white vine vinegar with a hint of black salt (not to mistake with baked salt that is black in appearance).
The cheese flavour that you are tasting is the part of "cream". It's Lactic acid. You know, the one you are producing when sweating and then complaining you smells like onions OR sour milk.
So, anyway. If you want to make a dip what you need is sour cream. Sour cream can be bought or made from regular cream by adding either vinegar or citric acid. Then you want to add spring onions. Remember that the white part of onions are more sweet and have "lighter" taste than the green parts. So use that to balance the onion taste and counter acidic of vinegar.
And, if you want to make it taste more oniony just use onion with a sharp taste. Put it in a hot place (or bake it for few second over a fire) and then mince it raw. Or juice it out and use the liquid.
If you taste it later and there will be "not quite this" it will be the umami flavour. Don' be afraid to use MSG to get that or if you want to avoid it use Maggi or few drops of soy sauce.