Yeah I get that, but he said that he is getting 18v on the cap. My solution was tailored to the middle ground, in that most of his high current loads are nasty like 12v DC motors and short circuits (which is why he has blown 5 ICs), and an assumption that if he needs perfect regulation it will generally be a lower current load and/or a lower voltage.
I know where he's coming from as my 5.5A bench supply get used for similar nasty loads, testing automotive gear etc, motors, charging batteries, and over 25 years the amount of times I have needed to use it for full 5.5A at max output voltage AND with perfect regulation has been exactly nil.
Making his supply perfect (ie adding good current regulation) would involve quite a bit of complexity and/or more Vin voltage headroom, so I suggested a reasonable tradeoff for his specific needs that *should* save him from more LM338 losses.