As usual, trickier than the video suggests. In addition to these notes, also check notes on similar power supply installs.
1. It is very hard to disconnect the optical sensor cable from the motherboard. There's no hidden catch, you just have to insert your spunger/thin screwdriver blade between the fittings and gently twist. I used a surgical clamp to also pull on the cable -- that did it. (The cable is being replaced, so you don't need to worry about it).
2. The top right screw is hard to remove. I had to partly remove it, then lever the power supply up as in the video while continuing to loosen it.
3. I used thin wide screwdriver blades to disconnect the power supply connect, my spudger wasn't rigid enough.
4. The supply has clearly been used before. In the context of something this old "new" means Apple refurbished. That's fine.
5. Beware the optical sensor, it's glued to the power supply. Look for it. When you insert the new supply place it first.
I seemed to succeed - until I discovered my optical drive had broken. Disks do not mount, after some tries they eject. There was a LOT of dust inside my Mini, I think some got in the optical drive. A cleaning DVD and compressed gas didn't fix it. I wonder if it would be wise to seal the opening to the optical drive -- certainly before cleaning.
This was a failure for me, even though the memory and drive change went well.