Don - KM4UDX
John -- do it the reverse. Start with an old 15-20v laptop power supply. Put a 2a fuse and drive the finals direct from the laptop brick voltage. Use the buck converter to generate 12v for the board from whatever the laptop brick squrts out. I added a simple LC ripple filter (used in RC drones) to the 12v output, but it made no detectable difference to anything I could observe. With 17v, I get ~28 watts on 80m, and the normal 3 watts on 10m. Good enough for all the digital modes, and yes, marginal for SSB DX, says me. Others disagree.
Increase the size of the heat sinks, or go active if you up the final voltage. Not that the finalls need it in normal operation, but to cover a likely bone-head move by the operator. Don't ask me how I know this.
In anycase, it is (largley) over driving which generates spurs and uggly bits. Not the PSU ripple.