From my research, the makers of Cardio C, actually source their C from Dalri, Scotland. It is called Quali-C. Quali-C is the brand of vitamin C that the manufacture makes (DSM). I was told by the people at Cardio-C that vitamin C can only come from one of two places. Either China or Scotland. They get theirs from Scotland. https://www.dsm.com/products/quali-c/en_US/about-quali-c.html
To confirm that, even If you notice on the packaging of the vitamin C powder here https://www.vitamincfoundation.org/powder.php
(the same powder used in Cardio-C), it is also the "Quali-C" product.
Here's the point: Doctor's Best brand of vitamin C is also sourced from the same exact plant in Dalri, Scotland. Although Doctors Best doesn't say that it is L-ascrobate on the label like Cardio-C does, I called Doctor's Best and they assured me that it is L-ascorbate. They told me that the Quali-C brand from Scotland IS L-ascorbate.
Cardio-C and Doctor's Best is the same stuff. Doctor's Best is about .05 cents per gram. Cardio-C is about .49 per gram on auto-ship, including shipping. In other words, Doctor's Best is nearly 10 times cheaper than Cardio-C.
Please, someone correct me.