Great job on the plasma rifles. When upgraded with the two sets of aligned cylinders it looks like the original concept art and the cool real-life replica prop:
http://img.izismile.com/img/img3/20101019/640/nice_handmade_fallout_640_03.jpg
http://images4.wikia.nocookie.net/__cb20080916232451/fallout/images/9/90/F3_Plasma_Rifle.jpg
http://www.flickr.com/photos/ryanpalser/sets/72157623717376540/with/4832756121/
And that connecting hose on the dual-cell harness makes all the difference.

I think that the Multiplas RIfle should come with those dual cells as standard. Perhaps get rid of the tape that makes the dual-cell harness look a bit makeshift and jury rigged, instead have a metal ring or something. The Multiplas has a massive capacity (in the vanilla game it is 60, compared to 24 of a normal rifle), and yet seemingly is powered by just one ordinary microfusion cell.
I think the Plasma Defender is another weapon where an extra battery upgrade should actually be part of the standard model rather than a weapon mod, because the Plasma Defender has a capacity of 48 small energy charges, while the other energy pistols use identical packs of batteries and they have 30 or 32 charges. Also, the Plasma Defender looks like the Extended Capacity version of the Fallout 2 plasma pistol, so putting an extended capacity mod on an extended capacity weapon seems a bit odd. (I guess the idea of the Plasma Defender is that the extended capacity modifcations have been repurposed so that it uses the extra ammo for more powerful shots instead of more shots per reload.)
In the case of the ordinary plasma pistol... I'm not sure the plasma pistol needs an extended capacity or "extra battery" mod. It already has a capacity of 16, which is pretty nice. (If anyone ever complains about the plasma pistol being rubbish compared to a 10mm pistol or a 357 magnum, their complaint will never be about the ammo capacity!) I'd rather have a magnetic accelerator, so a fully upgraded plasma pistol has a glass green tube for increased durability, surrounded by a flashing magnetic accelerator, and with extra injector/coolant things on the back for increased rate of fire.
Alternatively, could have a mod that increases the damage... so far none of the plasma weapons have any sort of equivalent to laser Focused Optics or a magnum's Long Barrel. (Heh, now I'm imaginging a plasma pistol with a really long glass tube, could look awesome, or could look very silly.)
Obviously it is hard to mess with the damage stats prior to Obsidian releasing the patch which is going to change the damage of energy weapons.
That's why I made them.

And that's why I suggested it!

Though I must give credit to Weijesen who first implimented something similar in EVE. The glowing bits on his weapons might have been a little over the top, but the green glass tube was good common sense.
I must point out that the term "Aperture Stabilizers" doesn't really make sense on the plasma pistol, as it doesn't have any apertures!

I've always figured those cylinder things (on both plasma pistol and plasma rifle) are some sort of coolant system, or heatsinks, or capacitors, or injectors. (Injectors is a handy catch-all term because it is non-specific as to what it is injecting. Could be injecting plasma gas, could be injecting electricity, could be injecting coolant.) And any of those would explain why altering them or fitting more of them would increase the rate of fire.
In Mothership Zeta the note about the unique Novasurge plasma pistol says that most of its weight is from the "coolant coils".
And then there's the Plasma Caster, which has an upgrade for "HS Electrodes" which attaches to the three bronze cylinders on top of the caster, so apparently the cylinders on a plasma caster are electrodes. So I guess that's five options then... "coolant coils", "heatsinks", "capacitors", "injectors", or "electrodes". But "Aperture Stabilizers" just means... a system for keeping holes balanced?