You can buy a lot of energy weapon ammo from the ncr shop in the hoover dam. I used the gattling laser and gause rifle almost exclusively the last 5 or 10 levels of my game and never ran out of ammo. Infact I had to give a lot to my companions.

If you are going all energy weapons raise your science and repair skills. Build weapon kits. Take the energy recycling perk. Get the jury rig perk. Use overcharged and max ammo when you have enough.

I can't remember her name but get the companion at the 188 rest area, give her good armor. She works like a bench so she can recycle ammo, improve ammo, and make those weapon repair kits.

I played through the entire game using mostly energy weapons and by the end I found normal mode a little to easy. Early on (say the first 5 levels) I used regular guns some just because of lack of ammo. Towards the end I raise my unarmed skill because I got tired of crippling myself when enemies got to close. Although this stopped happening once I got my power armor and gause rifle.

Her name is Veronica.

Speaking about Energy Weapons, well to me they are underpowerded and too common in the Majove. Current situation makes BoS look like idiots with theyr usless EW compared to GUNS. Maybe becouse they are "Still in the Dark"

The best you can get in terms of damage with EW is to use YCS/186 with Max Charged MF.