"Yeast energizer" is probably DAP or diammonium phosphate, which is pretty much meth for yeast. It's great for getting yeast to finish a big beer, but it's not really what you want for yeast starter unless it also contains nutrients and/or yeast hulls. You're trying to build yeast health, not just get them to work faster/harder. Yeast hulls is just dead yeast which the yeast will scavenge for micronutrients. DAP really isn't helping in a low gravity starter wort which the yeast can easily ferment anyway.
my ld carlson yeast nutrient says mad of food grade urea and diamond phosphate. my ld carlson yeast energizer says made of diamond phosphate, springcell, magnesium sulphate. the previous comment about the names and what its made of is "frustrating" seems appropriate. wyeast yeast nutrient says it has A blend of vitamins, minerals, inorganic nitrogen, organic nitrogen, zinc, phosphates and other trace elements that will benefit yeast growth and complete fermentation.
like the others, im left confused on what brand to use and how they differ.