where did you find the layout of the PSU?
I assumed that the OP had the Desktop Form Factor version of the ThinkCentre M55 based on the link the OP provided. Please excuse me if my assumption is wrong.
There is also a tower version and an ultra slim form factor model.
Maybe the OP should post the exact model number or form factor of the system they have.
I Googled on ThinkCentre M55 power supplies and found images of the internals of the desktop unit and its power supply.