Sounds like they don’t really know the issue at all as they are telling you different stories here.
While not easy you can repair the power switch if that is truly the issue. But the power supply is a sub assembly internal of your system and can be replaced on its own. Which sounds like what you did.
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But lets go back to your original power supply and really do the proper diagnostics to isolate out what is the problem as your just as lost as the person who gave you the story.
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But lets go back to your original power supply and really do the proper diagnostics to isolate out what is the problem as your just following what the person who gave you the story told you.
Plug in the AC power and if you have a MacBook Pro, plug in your system to the MagSafe connector what is the color of the MagSafe Plug Free or Amber or nothing?
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If you don’t have a MacBook Pro to test this can you give us a bit more here when you press the power button do you hear a fan running? Do you see any flicker of light from the display?
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When you connect your system with the display cable and go into the display control panel does the display show up? If it does take a flashlight and rest it on the displays glass at a sharp angle (15 or so degrees up) do you see a faint image of your desktop and its icons?
Sounds like they don’t really know the issue at all as they are telling you different stories here.
While not easy you can repair the power switch if that is truly the issue. But the power supply is a sub assembly internal of your system and can be replaced on its own. Which sounds like what you did.
But lets go back to your original power supply and really do the proper diagnostics to isolate out what is the problem as your just as lost as the person who gave you the story.
Plug in the AC power and if you have a MacBook Pro, plug in your system to the MagSafe connector what is the color of the MagSafe Plug Free or Amber or nothing?