This is from an earlier post:
"You can definitely use eCart to edit the cart functionality in Power Store. If you have eCart installed you will see that the PowerStore cart object is available in the eCart object panel."
Since PowerStore uses local checkout, you need to have a SSL cert. Most people are uncomfortable entering any personal information without a lock symbol so I use them even with PayPal standard as soon as I ask for address info.
At $18 a year for the cert, it pays for itself the first time you don't lose a sale from someone that leaves because the lock is missing.