Thank you for this detailed an accurate manual! I would propose to change/shorten the manual with a jump from step 18 right to 44 (see the notes in this two steps).

See note to step 44 to easyly remove the power supply without dismantling the whole computer (as also suggested by philaro).

If you came here right from step 18 you may first jump to step 47 (the screws) and afterwards lift the power source a little to release the short AC-in cable (and then do steps 45, 46, 48, 49).