What is the best way to provide AC power to the ElectriFly Triton charger ? It looks like a great charger, but will it be necessary to spend $120 for the charger and another 70
for an AC power supply ? I have read about the 'PC power supply' method but I am not sure I want to risk any damage to a $120 Charger.

Then you're going to have to buy a $70 power supply. Really, either you build one from a PC power supply, or you go buy one. You can look around, and I have a little. I've seen several, from several sources, but the ones that can handle the current loads and supply "clean enough" DC power to the charger all cost $70 or more, sometimes much more.

You might find it cheaper to do what I did. Buy a seperate charger to use at home that comes with an AC cord. I picked up a Wattage duel output "park flyer" charger. Does Nicad and Nimh (no Li), I forget the cell max, but the biggest I wanted was 8 anyway (TX pack), and it has both AC and DC inputs.

search for 'cosel power supply' on ebay. $20 buys you an industrial quality 13 amp power supply.

Yeah it may be best to do that. It will cost less money and I'll have 2 chargers instead of one. I have an Intelipeak charger for my Rc car batteries, which
has a 12v 7amp power supply. Tower's sell it separately for $44, but says NOT to use it as a PS for the triton. ( I guess it can't push enough AMPs).
I suppose it would be fine with a smaller charger like the ElectriFly peak 400, (which costs about $30) and just let the triton serve as a field charger.

7 amps is fine for most smaller packs. what is your wattage requirement for charging? (just a refresher, watts = charge rate (amps) * # cells * 1.5) That power supply puts out 84 watts, so just keep it below 60 watts or so and that supply is fine.

unless you are flying some high cell count packs you won't hit that anyway with a 4/5 or 8 cell pack.

The best compromise for me is to just get a lawn mower battery (quite inexpensive) and then use a regular automobile battery charger to keep it charged. This gives me plenty of storage to take to the field and its easy to use at home off the battery using the charger only to keep the lawn mower battery charged.

I'd definitely suggest the Cosel power supply from Ebay as well. I tried converting 2 PC power supplies for my triton and somehow couldn't ever get them to work right. Plunked down the 20 bucks for the Cosel, stole the power cord from one of the now dead PC power supplies and I'm up and running. I've charged my 3300 Nimhs with no problem whatsoever. I do know that you don't want a power supply with too low of a voltage/amp output ratio. Some PS's can put out 12 volts, but only put out 4 amps, so be sure that your power supply is putting out enough of both.

I bought an Astro Flight 110 to 12V power supply for about $75 from Hobby Lobby. Sounds expensive but isn't so bad when you add it up. If you buy a car or motorcycle battery and charge it with a regular battery charger and then use it with your Triton It will work just fine. All this assumes that you already have a regular car battery charger. Some of the mortorcycle batteries that have enough capacity to do the trick will still cost you about $50. There are regular automotive batteries that cost less and will do just fine if space isn't a problem.

has anyone every tried just using a regular car battery charger as the power supply for their rc battery charger? I thought about doing this, but I didn't want to blow my charger to smithereens.

Don't connect the car battery charger directly to the RC battery charger! The output of the car battery charger is very "unclean", meaning lots of ripple in the voltage. That could damage sensitive circuitry in the RC charger or any other electronic device.

That's about what I figured. That's why I went for the Cosel supply instead.

Just get a lawn mower tractor battery. Very inexpensive and will provide adequate capacity for a days flying. Recharge it at home with a cheap automotive battery charger.