I wouldn't put 18-24 volts on any of my 12vdc ham gear. But, that's just me..
Hey, maybe my 150 watt VHF amp will put out 300w at 24v..?.
I have smoked some small 12vdc electronics using "12" vdc wall-warts.
The last one turned out the 12vdc wall-wart was actually putting out over 18vdc (no load).
Toasted a real nice cable TV amplifier..
I'm not sure what my dumb Sears 6 & 12 volt battery charger/starter supply puts out when open..
I'll have to check it sometimes. You've got me curious now.