As there are no "teeny tiny" black capacitors near the transformer on a C128D and capacitors rarely emit smoke, you may be referring to the diodes? Small black barrels directly below the transformer, pin coming out either side and a small white stripe around the body?
If so, these are the rectifier diodes. The exact type is not critical, they just need to have the correct rating of at least 100V 2A or more. And take note of which end has the white stripe. The new diodes need to be soldered in the same direction.
See attached picture.
Bryce.