Why there are still people making linear power supplies besides these really high end SMUs?
Why not SMPS+post regulator architecture? Less power dissipation, and comparable noise and ripple.
Anyway from a different chassis there is no way to get super clean power source, so for serious analog circuits, there will always be local regulators.
A comparable resolution can be achieved from a BK9110, which is a little bit more expensive per channel, but definitely much more powerful.
For me, I don't use 2.5V/3.3V/5V from PSU, I usually get them from USB, so I only need a 2 ch PSU. In this case, BK9110 is actually cheaper than SPD3kX per channel.