How to open Cinema Display power supply?
Someone did it.

There's no good way to open it. Use a Dremel to carefully cut around the seam until it was thin enough to crack apart.

There's one huge capacitor (Rubycon KXW 450V 150 uF) that needs to be discharged before the power supply will start up. 

Be careful, because it's charged to over 100 volts. Solder a 600 k ohm resistor across it to bleed off the charge a little faster.