I think most folks just run a pair of car batteries in series for those big loads with a charger in place to keep things up to snuff, but with the price of batteries today, a big enough switcher supply is more affordable.  A 24 volt supply is usually cheaper than a 28, sometimes by a lot, and you can adjust them up to about 26.5, no real reason to run 28 as there was only 28 when the aircraft engines were running, 24 when not.  Meanwell supply's are very radio quiet.

Charlie, W4MEC in NC