Yes, what is used in Portugal is "brandy" in the sense that it is distilled alcohol produced from fermented grapes. It is fairly raw stuff, about 70% to 80% alcohol. They use fermented grapes because that's what they have available - wines that don't meet the quality standards, and pomace after the press process. It isn't oak aged, colored brown or watered down to 40% (80 Proof) like the "brandy" we find in liquor stores in the States. It's "firewater" - a lot closer to Everclear or moonshine than a commercial product.
I've used Bacardi 151 rum to fortify several batches of port-style and sherry-style wines, with good results. The high alcohol level means you are using MUCH less to achieve a given change in overall proof (less dilution of flavor). The rum by itself has a very mild flavor - it blends well with just about anything, and when used with port is just not detectable - the stronger flavors of the port completely dominate the mixture.
I've also used Everclear with good results, but less often, as I can't buy it in Minnesota. A high-proof vodka would work about as well, I expect. The two criteria I have are 1) high alcohol level, so as to minimize dilution, and 2) no strong flavors that might clash with the wine. So I wouldn't recommend gin, or tequila, or Scotch whiskey. "Brandy" or bourbon whiskey would be a second choice, if I couldn't get vodka or rum.
Doug