The power supply is one of the trickier aspects of getting a working C64 rig, and it's not uncommon to spend as much on it, as on the C64 itself. You'll see a lot of "no power supply, untested" C64s on eBay because of it...in my experience those are all just actually dead (and maybe known to be dead by the seller, but the well-known problem with power supply availability gives them plausible deniability...but, maybe they also tried with a PS that kills the computer, which also happens sometimes with the original power supplies).
In short, necessity is the mother of invention and what not. The Commodore power supply was a unique beast, so there are no off-the-shelf replacements, so there's been an aftermarket for them for a long time and schematics of the old power supplies have also been available for ages, though having one that doesn't have a dangerous failure mode is an improvement.
In short, necessity is the mother of invention and what not. The Commodore power supply was a unique beast, so there are no off-the-shelf replacements, so there's been an aftermarket for them for a long time and schematics of the old power supplies have also been available for ages, though having one that doesn't have a dangerous failure mode is an improvement.