Open the cord winding flaps.

Heat the power brick's plastic casing with a hair dryer, and/or run a razor blade along the seam between the two halves of the casing, in order to weaken the adhesive. This will make it easier to pry the case open.

Insert your pliers and pry slowly. (Make sure they stay seated in the inside corners, or you may injure yourself or gouge the case.)

The cord winding flap will fall out.

Do the same on the other side.

Work slowly!