Most attempts to find Dell SupportAssist get redirected to this page:
http://www.dell.com/support/contents/jp/ja/jpbsd1/article/product-support/self-support-knowledgebase/software-and-downloads/supportassist

It's OK, I read enough Japanese to find the download link on that page.  The link is:
http://downloads.dell.com/serviceability/catalog/SupportAssistInstaller.exe

The downloaded file is named SupportAssistInstaller.exe

Installation fails because an array index is out of bounds.

Dell has a video showing how to install SupportAssist:
https://www.dell.com/learn/us/en/05/videos~en/documents~esupport-supportassist-installing-supportassist.aspx

The filename is aulancher.exe

Mostly, searching for aulauncher.exe finds SupportAssistInstaller.exe

I found an exception:
http://www.dell.com/support/home/jp/ja/jpbsd1/drivers/driversdetails?driverid=p6gvx

The version of SupportAssist Client is 1.2 which I think is rather old.

The download link is:
https://downloads.dell.com/FOLDER03665274M/1/aulauncher.exe

The filename is aulauncher.exe

It shows UI while downloading something, then stops showing UI but is still executing in the background, and then shows UI again when it finishes installating.

But there is no icon in the Start menu nor on the desktop.

Hey, while the installer was executing silently in the background, it executed a program named SupportAssistInstaller.exe

Does this mean that installation really failed but it was silent and didn't show the failure?

Something got installed, version 2.2.1.23, but there's no visible way to execute it.

Here is one file:
C:\Program Files\Dell\SupportAssistAgent\bin\SupportAssistInstaller.exe

But I think that's just the installer again.

Here is another file:
C:\Program Files\Dell\SupportAssistAgent\bin\SupportAssistAgent.exe

But actually that file is executing but I think it's a service and there's no UI.

I have a feeling there's supposed to be a folder named:
C:\Program Files\Dell\SupportAssist

But there is no such folder.

Aha.  In the Application log, there is an informational event, not an error event, for SupportAssistAgent, saying:
Installation Failed with return code : 1603

The Application log has an error event for MsiInstaller.  Yes, Dell SupportAssistAgent failed to install.  The log file is 3.8MB in size.  Does anyone want it?

Uninstallation of Dell SupportAssist 2.2.1.23 succeeded.

Formerly SupportAssist had been installed on this computer but later had been uninstalled.  I don't know what the old version was.