My brother in law said my retro shelf was a fire hazard, and I hate that he was right
He pointed at the 14 power bricks stacked on a plastic shelf in my closet and said "that's 300 watts of heat with nowhere to go," which I blew off until I touched one and it was hot enough to sting. Now I'm looking at metal racks and spacing everything out, so how far apart do you actually keep yours?
The fire hazard stuff creeps up on you because nothing bad happens for years and then one day it does. Same thing happens with phone chargers left under pillows, daisy chained surge protectors, dryer lint traps people never clean. We all run the math on "it's been fine so far" and forget that fine so far is not a safety plan. For the bricks themselves I keep mine at least a couple inches apart and try to stand them on edge so the flat sides get air, since heat rises off those wide faces. Metal rack helps a ton but you still want a little gap between the brick and the shelf, even a couple of pencils laid down as shims works. If one is hot enough to sting, that one is either dying or pulling way more than it should, so check the output rating against the device too.