Powering a bunch of strips from one wall plug - what worked for me

I ran into the dim far end problem on my staircase project last year. Eight metres of 24v strip split across three runs, and even with chunky feeder wire the last metre or two had a noticable warm tint on white. Ended up soldering injection feeds at both ends of each run and at the middle one, and the difference was instant. If I did it again I'd plan the injection points before sticking anything down, peeling strips off a wall to add wires later is miserable. One thing I'd add is to test the whole setup at full white brightness before you close anything up. I found a dodgy solder joint on my second run that way, it whould light fine at low brightness but flickered like mad when everything pulled hard at once. Much easier to fix when the wiring is still accessible. On the supply sizing, I did the maths like you said but ended up sizing bigger than the calculated number. My strips were rated at about 14 watts a metre and I built in maybe 20 percent headroom on a Mean Well unit, and it barely gets warm. Running a supply at its ceiling all evening seems like a good way to shorten its life, so I'd rather oversize than not. Mine lives in a cupboard with a bit of ventilation and has been fine for over a year now.

This lines up with what I saw on my shed conversion. I calculated the draw properly and still ended up going a size up on the supply, and it just hums along barely warm even after hours running animations. Also learned the hard way to keep the power wires away from the data line a bit, had wierd glitches til I rerouted them.

Worth adding that the data line matters too if these are addressable strips. I did 18 metres of ws2812b around my living room ceiling and had ghost pixels and random colours until I put a 300 to 500 ohm resistor on the data input at the first strip and dropped a level shifter in. Also plan your wiring channels, mine run behind a wooden trim piece so nothing shows.