vSphere Update Manager downloads patch definitions and notifications from online download sources.
By default, there are three download sources, namely ESXi updates, Cisco, and virtual appliances. You can also add a custom download source. This becomes necessary if your hardware vendor has system-specific updates.
The following procedure explains how to add a download source:
Connect to vCenter Server as an administrator using the vSphere Client.
Go to Home | Update Manager.
Navigate to the Configuration tab and then to Download Settings on the left pane.
Click on Add Download Source…:
In the Add Download Source window, enter the URL in the Source URL field and click on Validate URL. If the validation completes successfully, then it will show as Connected. Click on OK:
Once the custom source has been added to the list, click on Apply to save this configuration.