Hi Fernesto,

No, it won't affect another account's PST data. Do the same steps as told by gmayor and as you said while moving PST items into your existing Gmail account with Outlook, you're getting password prompt, in this situation to stop showing this prompt window, you need to enable less secure apps in your Gmail account settings.

If still doesn't work then de-configure gmail account from Outlook and then re-configure that account and then try to move the PST items.

Regards,
Anjlua