Quite often there is a huge discrepancy between the label rating on a power supply and the power it actually uses, on the input side, while its output ratings are likely to be reasonably accurate.
Picking one power supply at random I see:
INPUT : 100-240V(AC) 50-60HZ 1.5A
OUTPUT : 19V(DC) 3.95A
It's quite small and runs warm (but not hot) possibly dissipating 5-10W as heat.
So it supplies just under 20*4 = 80W and probably never consumes more than 90W sustained. That would mean 0.9A at 100V or 0.375A at 240V.
The input ratings are deliberately conservative, because their purpose is not to estimate your electricity consumption, but to ensure safety by encouraging you to budget your current to choose the correct fuse, breaker, and not overload the mains circuit.
The fuse rating has to cope with the inrush current, which may exceed 1.5A but for such a short time that the fuse will not blow. This explains why one current rating is given despite the huge range of input voltages. If you have fused cables, a 1A fuse will probably not last, but a 3A fuse (the next standard value in the UK) will.
If you add all the rated loads on an extension cable on a 13A plug, they should come to less than 13A. If you add all the loads on 13A plugs on a 30A circuit, they should come to less than 30A. Given the expected current for a circuit, you can choose the appropriate wire gauge, and so on.