Not sure I’ve ever heard of an embossed triangle can in the way you describe it, but I’d steer clear of a repainted one. The triangle cans you’ve found on the internet are from the Czech Republic. Mobiloil made one that I know of while Shell has quite a few (possibly more than ten). Sadly, according to a Czech friend of mine, they are now being faked, as well. Without a picture, though, I can’t say one way or another what you are taking about.
Looking for NJ oil company related items (Mohawk, Guardian, Whiz, etc), Invader, Bulko and Freedom items, and foreign Gargoyle and Sinclair cans