20V laptop power supply from four 5V+5A 'baby' supplies
Current sharing SMPS is ripe for instability with 4 feedback loops sharing the same output.  It is unlikely to be smaller than  single SMPs as there are redundant packaging and primary side functions.

Look for a better universal Laptop charger and you can reduce power needed by dimming the display and not using when recharging by 50% or expecting a slower charge time.