For example, when High Templar energy upgrade is researched, and you make a HT, it will start with 60~ energy (i think it is 65). So like to the rest of units that have energy. But, when you make a DA, no matter if the upgrade is researched or not, it will always start at 50.
I guess this is because of how DA are made (melding 2 templars instead of being produce out of a facility). It's a bummer considering how much energy maelstrom and mind control require. If it did affect them, you could pre-research energy upgrade (while you have a couple of dark templars being sneaky around the map, and meld them as soon as the upgrade is finished) to start with some head energy and research maelstrom/MC while you wait for the energy the spell needs (yes, that was theorycrafting).
PD: was going to make a topic about this, but thought there isn't much to talk about it...
PD2: another curious thing about DA that was discussed in a thread (regarding Rock vs Chalrenge tie) was that when you MC a DA, the DA you get starts with 0 energy. Seem reasonable considering that if not you could chain all your opponents DA with MC and it would turn into a "the one that shoots first, wins" situation. Credit to the guy that checked this... don't remember his nick...