Is there a way to create automatic "broken" bar charts either in
PowerPoint or Excel (and brought into PowerPoint)? I have a bar chart
with some wildly varying values (from $500 to $500,000) and when I
create a chart, with $500,000 as the max value, the lower numbers are
barely visible at all as bars.

So far, I've faked it, by putting in some dummy values on the data
sheet, altering the max value and manually placing a broken line on the
upper value bars, but is there any native way to do it so my client can
adjust values himself?

I think I recall a function like this when I used Delta Graph years
ago, but I'm clearly not using Delta Graph here.