Life Extension has long sold CoQ10 ubiquinol combined with shilajit. (They sell ubiquinone, the less-absorbable form of CoQ10, also, and ubiquinol by itself without shilajit). Here's what they have to say about shilajit:

Shilajit enhances CoQ10 effectiveness

Shilajit is a nutrient discovered in the Himalayas. In preclinical models, shilajit has been shown to promote mitochondrial energy production and increase adenosine triphosphate (ATP), which is the main source of cellular energy.15,16 The combination of CoQ10 and shilajit produced a 56% increase in cellular energy production in the brain—45% better than CoQ10 alone. Muscle tissue saw a 144% increase in ATP, more than 50% better than with CoQ10 by itself.15