Fast and simple binary concatenate files in Powershell

The approach you're taking is the way I would do it in PowerShell. However you should use the -ReadCount parameter to improve perf. You can also take advantage of positional parameters to shorten this even further:

gc File1.bin,File2.bin -Encoding Byte -Read 512 | sc new.bin -Encoding Byte

^{Editor's note: In the cross-platform PowerShell (Core) edition (version 6 and up), -AsByteStream must now be used instead of -Encoding Byte; also, the sc alias for the Set-Content cmdlet has been removed.}

Regarding the use of the -ReadCount parameter, I did a blog post on this a while ago that folks might find useful - Optimizing Performance of Get Content for Large Files.

It's not Powershell, but if you have Powershell you also have the command prompt:

copy /b 1.bin+2.bin 3.bin

As Keith Hill pointed out, if you really need to run it from inside Powershell, you can use:

cmd /c copy /b 1.bin+2.bin 3.bin