Capacitor Tester and Reformer Unit - Stefan Niewiadomski

[Terry]

What is the best way to determine which is the inner and outer foil on modern capacitor (other than electrolytic)?

This is pure guesswork but, if it is important, why not try wrapping some tinfoil round the cap and then measure the capacitance between each connection and the foil?

If the difference in the readings is too small for certainty, try injecting a signal into the capacitor, then look for a signal between the foil and the earthy side of the source. Repeat with the capacitor connections reversed to see which way round produces the lowest level. 

I don't know if either of these will work but it is worth trying them as an experiment.