There's a difference between Energizer and Nutrient. Energizer contains some extras (typically) like vitamin B and some oddly named phosphates plus other things I can't think of right now. These are typically used to kickstart stuck fermentations by adding in some "Red Bull" for yeasties.
Yeast nutrient provides primarily nitrogen. (and some other scientific-y things) Nutrient is usually used in the beginning to provide some additional "nutrients" that are lacking in the must/juice/wort.
Boiling yeast and adding it to the beginning is supposed to be helpful, but I've personally never tried it. It's pretty cheap stuff, so I just buy it from the LHBS and leave it up to the pros.
Boiled (dead) yeast, diammonium phosphate, magnesium sulfate, vitamin B complex. I'm sure there are other things that go into commercially produced yeast energizer, but those are the main ingredients.
Regards, GF.