Digital DC DC Converter for Power Control
Building your own will be the most robust way to do it, but it is not easy. I can point you in the direction of good places to start if you're interested. Will require a good understanding of magnetics, but it is not too hard (as long as you don't care about EMI or PF).

In any SMPS you will have some sort of voltage feedback. This is where that potentiometer comes into play, it varies the resistive divider used for the feedback. This signal is compared against a set voltage reference, usually a LM431 or something similar. 

If you find a COTS power supply at 28V@10A you can then remove this voltage reference and instead wire up a I2C DAC, or an I2C digital resistor in place of the pot. You will need a very low drift IC for either of those.

It sounds easy, but there is no guarantee it will work. Consider the SMPS you buy is a buck converter. If you lower the voltage too much, the duty cycle needed to create that voltage will become very low and regulation will suffer. Same goes for too high of a voltage/duty cycle. This is mainly a concern for cheap supplies where the devices are designed for a very specific operating point and will fall apart outside of that. If you find a supply that works well at your range by adjusting the pot then it should be fine when controlled digitally.

The error amp, which is the "filtering" for the voltage feedback signal will be connected to the pot and its other pin connected to the reference. Should be fairly easy to find.