normal pi 4 with screen draws 2.5 A your hat will pull something to so with 3A will be on the lowside…
but you could split it with ( not with a y - cable) but with 2 power supply’s… splitting a already low power supply wil give it less instead of more… and that will end in a boot loop
or use a high enough power supply like a 5A that gives a lot the chinees power supply are mostly not so good…the cheap ones…