That sounds very correct.
The math is like this you need 360W + something to cover heat losses. So lets say 450W (this allows as low as 75-80% efficiency). Then you get 110V (and perhaps it goes a bit lower at times - so lets say 100V).
How many amps does a 450W load use at 100V? W/V = A, so 450W / 100V = 4.5A
And thus a 5A to 6.3A fuse will allow the power supply to operate even under non-optimal conditions, but will still protect wires, connectors etc. quite well, so even wimpsy 110V wiring will not over heat in case of a short (or internal breakdown) in the power supply.
You will want as slow fuse, as capacitors inside the power supply might draw a substantially higher amperage, for a few milli seconds, when you turn the power supply on. And a slow fuse will allow this to happen.