Unplugging (and leaving the plug a few centimeters out of the wall, not just "pull out until it turns off") is practically 100% safe at preventing "unwanted input from the power line" coming in; but depending on your goal, it may be more than needed (a single pole switch is sufficient for eliminating power usage, for example)
I've heard that each outlet draws the same amount of power, so it's dangerous to have say a power strip in one outlet and a single device in the other.
Uh? No, a socket by itself doesn't consume anything (assuming we are calling a socket a socket, not those fancy timers/solar/motion controlled kinds), the watts or amps written on them are the maximum safe load (and that number assumes not only the wiring on both sides is up to that spec, but also that the connectors are not worn out!)
A loaded socket will result in some power consumption, since (at room temperature and pressure, with the metals commonly used
) it's not an ideal conductor, so it has non-zero resistance, therefore it generates heat proportional to the resistance (that's why loose sockets combined with large loads are dangerous)
the switch doesn't use ground, does it? there's no prong for it.
You tell me, never seen one
The power brick is most likely
class 2 - check the logo - and the console itself class 3; neither require a ground (as far as safety is concerned; there may be other "minor" issues, like the famous shocks from touching a metal Mac if you use the ungrounded plug of the 2 included ones, or regarding internal surge/noise protections)
do you mean to say that damage caused by a faulty cable is extremely unlikely to cause some sort of short or feedback damaging a device?
Pretty much: a short* caused by a loose socket is practically impossible and wouldn't damage the load any more than a non-shorting loose connection, while dropouts may do (inductive spikes causing excessive voltage, insufficient average voltage resulting in overcurrent while attempting to maintain a constant power, ...) but I'm not sure how likely these problems are with a relatively light load as a Switch charger (it is mainly inductive, which could be a disadvantage)
* strictly speaking, a short circuit is a 0 ohm connection, which would result in energy running in a loop to and from the power company for free** - but that's impossible (see above comment on materials and temperature) and everyone accepts the common-sense-adjusted definition!
** the 2nd principle of thermodynamics does not actually say that energy circulating in an infinite loop is impossible - "only" that it's impossible to add or remove some without inefficiencies