I want to draw 20 amps from my home power outlet is there any way to do that safely?
Not a problem. You have 40 devices drawing 0.5 A each at 5 V. 

40 x 0.5 A x 5 V = 100 W

So if your AC to DC converter is 100% efficient then you need to draw 100 W from the mains and in the US that is I= 100/120V = 840 mA which is well within the limits.