I notice that when I am wearing the Ranger Combat Armor that I don't have the same factions and rep levels that I do if I take it off and wear a non NCR faction armor. For example with it I don't have the Great Khans on my list (but show them as Neutral on the map locations) and I am Neutral with the Powder Gangers on both the list and on the map locations. If I take it off I get the Great Khans back on my list with Soft-Hearted Devil (which is the right rep) and I get my Villified with the Powder Gangers. The weird part is yesterday I had teh NCR on my list with the Ranger Armor equipped at Liked rep....when I started my game up today the NCR is not on the list anymore (but the map locations show Neutral). If I take the armor off I get the NCR back on the list with Idolized rep. This sounds like a bug if I ever heard one. I have not used any of the debug console cheats nor will I. Also I did not do any quests between yesterday and when I started the game today to have had my NCR rep drop with the armor on. Any help would be great.

Faction armor is definitely meant to alter reputation with different factions, but the implementation seems quite buggy.

There is definitely a bug with some faction armor. I'm in the Ultralux kitchen trying to complete Beyond the Beef and Pheeble Will and I had Veronica randomly tell me off for fighting the Brotherhood when I had been liked by them. After experimenting a little I found out that the White Glove Society Mask that I had just put on reset a bunch of my faction standings when I put it on (I checked before and after) yet when I took it back off they stayed at their lower level. Needless to say I won't be putting that back on.