C:\Windows\System32>chcp 1251
Текущая кодовая страница: 1251

set NLS_LANG=AMERICAN_AMERICA.CL8MSWIN1251

C:\Windows\System32>sqlplus "/ as sysdba"

SQL*Plus: Release 11.2.0.4.0 Production on Wed Sep 9 18:43:06 2020
Copyright (c) 1982, 2013, Oracle.  All rights reserved.

Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL> select dump('тест') from dual;

DUMP('ТЕСТ')
-----------------------------
Typ=96 Len=4: 242,229,241,242

  [Console]::OutputEncoding = [Text.Encoding]::Unicode 
$OutputEncoding = [Text.Encoding]::GetEncoding(1251) 

  chcp 1251
  set NLS_LANG=AMERICAN_AMERICA.CL8MSWIN1251
  
  $sqlPlusCommands = @"

select dump('тест') from dual;

exit
	"@

  $sqlPlusCommands | sqlplus "/ as sysdba"

PS C:\>   [Console]::OutputEncoding = [Text.Encoding]::Unicode
PS C:\> $OutputEncoding = [Text.Encoding]::GetEncoding(1251)
PS C:\>
PS C:\>   chcp 1251
Текущая кодовая страница: 1251
PS C:\>   set NLS_LANG=AMERICAN_AMERICA.CL8MSWIN1251
PS C:\>
PS C:\>   $sqlPlusCommands = @"
>>
>> select dump('тест') from dual;
>>
>> exit
>> "@
>>
PS C:\>   $sqlPlusCommands | sqlplus "/ as sysdba"

SQL*Plus: Release 11.2.0.4.0 Production on Wed Sep 9 19:17:17 2020

Copyright (c) 1982, 2013, Oracle.  All rights reserved.


Connected to:
Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options

SQL>
DUMP('OANO')
----------------------------
Typ=96 Len=4: 111,97,110,111

SQL> Disconnected from Oracle Database 11g Enterprise Edition Release 11.2.0.4.0 - 64bit Production
With the Partitioning, OLAP, Data Mining and Real Application Testing options
PS C:\>

  [Console]::OutputEncoding = [Text.Encoding]::Unicode 
$OutputEncoding = [Text.Encoding]::GetEncoding(1251) 

  set NLS_LANG=AMERICAN_AMERICA.CL8MSWIN1251
  
  $sqlPlusCommands = @"
  
  @after.sql

exit
	"@

  $sqlPlusCommands | sqlplus "/ as sysdba"