问题
This issue has been there for a while now. My internet connection is very good. However, I am unable to download any VS marketplace extension. I am able to get all extension lists from VS, but always unable to download it from Extensions -> Manage Extensions or even from VS marketplace website
回答1:
I am able to get all extension lists from VS, but always unable to download it from Extensions -> Manage Extensions or even from VS marketplace website.
When you click the Update button in VS Extensions Manager UI, it actually downloads the xx.vsix from VS Marketplace website. So I think the root cause is that you can't download the extension from the website, and it could be something wrong with Internet Connection. You can try to access the marketplace website with IE browser to check this point.
I assume this issue is similar to Error caused when trying to Installing package in .Net, it might be something wrong with your DNS or proxy, or maybe the settings in your firewall corrupt the download. I think that's why your Internet is good but can't access the website well.
And if you can't resolve the Internet issue in short time, I suggest you can try to install the extension you need by another machine which can access the website successfully. An extension is a xx.vsix package, you can install it from the website by another machine and copy the xx.vsix to your current machine, double-click it to install or update automatically. (And if it works, it actually indicates something is wrong with your Internet.)
Hope it helps :)
来源：https://stackoverflow.com/questions/57861943/unable-to-download-any-microsoft-visual-studio-2019-extension