I was able to successfully download a file with puppeteer, but it was just saving it to my /Downloads folder. I've been looking around and can't find anything in the api or forums to set this location.
My downloads are basically just go going to the link:
await page.goto(url);
This is how you can set the download path in latest puppeteer v0.13.
await page._client.send('Page.setDownloadBehavior', {behavior: 'allow', downloadPath: './myAwesomeDownloadFolder'});
The behaviour is experimental, it might be removed, modified, or changed later.
Pst, you can try more tricks listed here, on your own risk :).