The two foundational supplements, Advanced Mitochondrial Formula and Metaphenol-27, have about 190 mg Acetyl-L-Carnitine. Would adding another 1000 mg be safe and advantageous?

This would be safe and, as you noticed, a number of other supplement makers are now offering capsule formulations of a 1000 mg dose for this ingredient and that is because it has been shown clinically to be advantageous and safe as well.