Shortest Script Challenge - Alphabet staircase

#Shortest Script Challenge - Alphabet staircase
#https://www.reddit.com/r/PowerShell/comments/7rwxmp/shortest_script_challenge_alphabet_staircase/

#My attempts...
$a="A".."Z";$i=0;Do{-join($a[0..$i]);$i++}while($i-ne26) #56 Initial attempt, typed it out exploded then just removed white space.
$a="A".."Z";$a|%{-join("A"..$_)} #32 A bit more refined.
("A".."Z")|%{-join("A"..$_)} #28 Who needs $a?
65..90|%{-join("A"..[char]$_)} #30 Trying a different take, not as good.

#/u/vrdse
0..25|%{'ABCDEFGHIJKLMNOPQRSTUVWXYZ'[0..$_]-join''} #51
0..25|%{('A'..'Z')[0..$_]-join''} #33

#/u/nadroj_r
0..25|%{[char[]](65..90)[0..$_]-join''} #39

#/u/bukem
65..90|%{-join(65..$_|%{[char]$_})} #35
0..25|%{-join('A'..'Z')[0..$_]} #31
('A'..'Z')|%{-join('A'..$_)} #28 Yay, same as my 28.

#/u/bis
('A'..'Z')|%{$z+=$_;$z} #23
$z='';('A'..'Z')|%{$z+=$_;$z} #29
$z='';65..90|%{$z+=[char]$_;$z} #31

#/u/Jarmom
65..90|%{$x+=[char]$_;$x} #25 Need to "remove-variable x" to rerun.