I just started EndoAmp (a PS supplement) about a week ago. The serving size is 800 mg per scoop. It's expensive (about $50 a pop for 29 servings no matter where you go), but I'm noticing a difference right away. I feel great (definitely less stressed) and have noticed reduction of fat in some of the typical cortisol regions (midsection, face). And that's just in a week. I highly recommend it.
There's been studies about PSerine's effectiveness. But you need adequate dosage. I think 800mg is a good baseline. And for the price EndoAmp is the best way to go. I looked up individual supplements from NOW and such, and to match the dosage, you're going to be paying out the ass.
So if you have the cash, I say definitely worth it.