Slacker, extended power supplyI got mine at Costco. its called a 3 in 1 Power Station, it has battery clips for jump starting your car, a 12v outlet, a light and 200 psi air pump for the inflatable doll. You can charge it from a wall outlet or from the cigarette lighter in your car. If I remember correctly, it cost about $60 to $70.
There are a lot of similar products, I read of one in a thread here that had its own 300 w AC outlet built in, which would work for the Sager power brick. I got a Coleman P300 inverter ($60). True, the output power isn't a true sine wave, but I trust the brick to deal with that. What comes out of it is nice clean DC.
You could also just get the Sager DC adaptor and save the inverter, I just happened to also want to be able to use the power supply for other stuff as well so it made sense to get the separate inverter.
Caution, as with all power supplies, you need to condition them regularly. But that's not to much of a problem. I do it as part of my monthly conditioning of my UPS system (4 x 350 units) and in a bad power outtage, I would plug them into the Coleman/Power Supply to keep all my stuff running.
As I said, its not what I would consider real 'portable', but when mounted on the folding luggage cart, its not a problem in most cases. I do get some strange looks while dragging it across the lawn at Waimea or Kualoa beach parks, but what the heck. Like I said, there's plenty of room on the cart for the laptop, reference materials, lunch, a cooler, whatever. A couple of times I have also plugged my electronic cooler in to it as well, while running on the internal battery. Hint: Get a cart with the biggest, fattest wheels you can find. There are a couple of manufacturers that make a power supply with its own cart which would be handy, but they also charge for the convenience.
I do make sure I run off the power supply first, just in case it runs down, then I have at least an hour on the internal battery.
Hope this makes your day.