It's complicated. But I think it's important to note here that, pre-ACA, the American system had two major flaws - high cost, and incomplete coverage. The ACA chose to address coverage first, rather than cost. The CDC reported the results here:
"More recently, the percentage of uninsured adults aged 18 to 64 decreased, from 22.3% in 2010 to 11.9% in the first 3 months of 2016. During this 6-year period, corresponding increases were seen in both public and private coverage among adults aged 18 to 64."
"More recently, the percentage of uninsured adults aged 18 to 64 decreased, from 22.3% in 2010 to 11.9% in the first 3 months of 2016. During this 6-year period, corresponding increases were seen in both public and private coverage among adults aged 18 to 64."