Building a High Current Power Supply? (Odd Voltage)
Building a 28.8 Volt @ 30A power supply (> 860 Watts) is not a trivial exercise even for an experienced power supply design engineer. Getting it to be accurate to 0.1V (+/- 0.35 %) probably doubles the challenge!!

This would not something that you could successfully "hack together". 

I would encourage you to look around at some electronics equipment surplus yards to see if you can find a ready built 28V supply (28V DC was common in military, aerospace and some communications applications). Look for a high power linear power supply. These are usually adjustable (or can be modified to be adjustable). Linear power supplies can be adjusted up and down by a volt or so to get to your unusual voltage requirement.

One name to look for is Lambda. If you find the type of thing I have in mind it would likely look like this: