As for (1), unless you specifically go purchase a quality PSU, the PSU you get in a pre-built machine is usually utter trash as far as output quality is conside

As for (1), unless you specifically go purchase a quality PSU, the PSU you get in a pre-built machine is usually utter trash as far as output quality is considered. (This is probably a fault of the ATX standard, which frankly allows too much leeway. Many parts that could otherwise use the voltages provided by the PSU have to include their own power regulation circuitry simply because the direct PSU output is too noisy) It's a good idea to build your own computer from newegg or similar just to know the PSU you'll get. Other than that, there's no difference if the SSD is plugged in by "a trained professional" or yourself.