Just remember, most small dry chemical extinguishers are NOT rated for putting out solid combustibles (wood, paper, cardboard, plastic). If they are, the rating is very small. Most of them are rated for putting out liquid (grease) or electrical fires. BC rated extinguishers are only rated for liquid and electrical fires.
If you do have an A rated extinguisher, it's A rating will be much smaller than the BC rating. Something like 1A:8BC means it's solid fuel rating is only 1/8th the B rating.
A rating: solid fuel (wood, plastic, paper)
B rating: liquid fuel
C rating: electrical fire
MUCH more effective against solid fuel fires is a connected garden hose.
Ken