24V psu in your case can be 60W, 120w. it doesn't need much. It's running IO and the Z brake release and little else. If you had an ATC with solenoids and coolant valves etc, you might need to upsize.
My little machine in that video runs a 240W 24v psu for the control AND the axis servo power (180w x3). Should be using a 480 really, but it still barely gets warm. The DIN psu's are rated to spec unlike the cheap little brick ones. When it says 120w, it MEANS 120w, full load, no sag, often with detailed overload specs. Mine for example can do 360w for 5 seconds every 30 and 480w for 1 second every 11 (just going on memory, its probably not quite that). It has a defined duty cycle just like the servos. The cheap brick psu's say 120w and MEAN "120w for 1ms before it catches fire". So there's a reason they cost a lot, not just cause of the mount.