The Half-Life wiki cites the AR2 alt-fire crate being available as soon as HL2, but I've yet to see one in the game. Do they exist at all? If yes, where they could be found?
Having replayed Half-Life 2 and both episodes recently, the energy orb crate (if it exists) makes no appearances.
I believe the wiki image is incorrectly labeled and actually shows a pre-Episodes AR2 main ammo crate. Note the icon on the side of the crate: for the other firearms, this icon shows the specific ammo type (note the distinctive shotgun shell icon, for instance). The side icon of the two AR2 crates are identical, showing that they are both AR2 regular ammo. The crate icon is also the wrong shape for energy orbs; their icon is egg-shaped, tapered on both ends, and features prominent vanes.