cat lill01.txt  

camel   42
pearl   94
dromedary       69

cat lill02.txt

camel   8
hello   12345
dromedary       1
perl    94

perl -lane "$r{$F[0]}+=$F[1]}{print qq($_\t$r{$_})for sort{$r{$b}<=>$r{$a}||$a cmp $b}keys %r" lill01.txt lill02.txt

# or shortened by one char because perl -a implies -n

perl -lae "$r{$F[0]}+=$F[1]}{print qq($_\t$r{$_})for sort{$r{$b}<=>$r{$a}||$a cmp $b}keys %r" lill01.txt lill02.txt

hello   12345
pearl   94
perl    94
dromedary       70
camel   50