Last week when I printed out my labels with dc it said the cost was 0.00.  This week once again I am being charged .19.  Does this mean they will not charge me at the p.o.??

For First Class Mail, DC is free.

For Media Mail, it is 19 cents.

Was the free one a lighter book that went First Class, possibly?

If you are printing labels with PBS printable postage (and e-DC) there should be no charge for the e-DC portion.

If you are printing labels with PBS e-DC only, there should be a .19 PSPS charge ... regardless of what the suggested postage on the label says.  TPTB have apparently been working on the programing, but it doesn't consistantly add the e-DC charge yet.

You will only have to pay the .19 once, though - this isn't a double charge.