How to export all users with all custom fields?
You can use the Drush Entity module:


  With drush entity you can query the entity system available for Drupal
  8, 7 and (some of) 6.


Getting all users with some fields:

drush entity-read user `drush entity-read user` --fields=uid,mail,name,created,access,login


Getting one user with all the fields:

drush entity-read user 1 --fields=* --format=json


Getting all the users with all the fields:

drush entity-read user `drush entity-read user` --fields=*


Getting some users with some fields:

drush entity-read user 1 2 --fields=uid,mail,name,created,access,login --format=export


Output (for the last command):

 1  mail@gmail.com  admin  1353518169  1470089957  1469713365
 2  other@gmail.com  webadmin  1353518169  1470089957  1469713365


If you want to try with another options you can read this page: http://build2be.com/content/drush-entity-support-patch-needs-review