An official RaspberryPi 5 PSU is akin to a 27W mini brick which doesn't block any adjacent sockets on a power strip. However, the power bricks came with my N100 systems are similar size to 60-80W MacBook power bricks, they're way bigger, even if they're not significantly more powerful.
No, N100 systems do not contain their power supplies in the box. They're external.
If you were to build it yourself, you can find passively cooled N100 Mini ITX motherboards (I own an Asus N100 Prime) which you can fit with a pico ATX PSU or HDPlex PSU. Pair with a SFF case, you could get it around the size of a mac mini without the brick. Maybe something like a skyreach case.
Again, too big for my requirements. What I want is a box I can forget until it breaks or I need something directly from it. RPi5 allows me to do that while handling a ton of workload for me.
Maybe the tasks it does are light from CPU/IO perspective, but the burden I offload to it is tremendous.
The N100 systems I have are desktop systems which spend most of their life powered off or at standby.
No, N100 systems do not contain their power supplies in the box. They're external.