TxtA2U

TxtA2U is a software application you can use to produce text documents with the Unicode encoding format from ASCII. It's a console-based tool that comes packed with simple, approachable commands.

Portable text converter with CMD support

Going through an installation procedure isn't necessary. TxtA2U is wrapped in a single file that can be moved anywhere on the computer or onto a thumb drive to effortlessly convert ASCII text on any PC without setup.
After calling the process from a Command Prompt window by entering the file name and extension, TxtA2U shows the syntax: TxtA2U.exe InFile OutFile [/y].

Set the source ASCII and output Unicode files

All you have to do is indicate the source ASCII file you want to convert, then set the output file name and hit Enter. If the source is in a different directory than TxtA2U, then make sure to specify its full path, and the same rule applies to the output document.

Confirm to overwrite existing files

The conversion operation doesn't take long, after which you can find out the size of the input and output files (bytes). This message can be hidden by appending the /q switch to the conversion command.
By default, TxtA2U prompts you for action when encountering conflicts about files with the same name, but you can give it permission to overwrite existing files using the /y switch. The syntax can be reviewed with the /? or /h switch, where there's also an example included to give you an idea of how it works.

Easy-to-use ASCII-to-Unicode converter

We haven't come across any compatibility issues with Windows 10, although the developer hasn't updated this program for a pretty long time. The ASCII converter carried out tasks fast while remaining light on system resources consumption. Thanks to its intuitive commands, TxtA2U can be handled with ease even by those with minimal experience in CLI utilities. Too bad that it cannot convert multiple files at the same time.
To convert Unicode to ASCII, you can use TxtU2A, another command-line application made by the same developer.