I remember the old recommendation from the early 2000s, but I'm not sure if it's still "a thing". Switched-mode power supplies reach closer to their nominal efficiency rating the more current you pull through them.
I have an anecdote: many years ago when Bitcoin/altcoin mining on GPUs was still feasible I ran a rig with a 335 watt TDP graphics card, and the whole setup measured 360-something watts at the wall outlet. It ran 24/7 for months on a 400 watt PSU, without problems.
In the case of power supplies, both total capacity and durability are indicated by the power rating. I don't know what current thinking is, but recall when overspeccing the power supply was often recommended for reliability and cooling considerations.