You want an inverter. Minimum 400 watt peak 800 watt. You can get one for under $30.
Just used one last week. The only power source at the barn is in a very inconvenient location. I have to drive my stuff up to it, wash my horse, saddle her and ride up to the power plug to clip her. There is no place to tie, and a bunch of crap laying around. The barn is well maintained but the power is kind of up by the border of the BOs part of the property where they have chickens and some other livestock.
Anyway, normally pony stands while I hold the lead rope and clip her but last week, I have no idea what was wrong with her. The chickens were making noise, there was some construction nearby, and a multitude of other distractions. Pony lost her brain and I spent over 2 hours trying to get it done and only suceeding in getting about 1/3 of her clipped.
A fellow boarder took pity on me before I committed equicide.She loaned me her inverter. The thing was awesome, I pulled my car up to ponies stall and clipped it to the battery, finished her up while she ate her grain.
I had considered getting a generator, but they are expensive, inconvenient to store and you have to deal with the gas. I hadn't considered an inverter because when I last looked at them (10 years or so ago) they were way to costly and didn't power much.
Bottom line, I'm getting one too!
Oh, dang, you asked about portable power supplies? I don't know how effective they are. They are batteries and batteries do wear out. Maybe someone else has experience with them.
I like the inverter idea it is about my price range.
I am fortunate to know people who recycle dead or nearly dead electronics and they will keep an eye out for me if I put a bounty one one of those battery pack things. I like the battery pack thing it is just out of my price range.
Can you just wheel a car battery out to the stall and use the inverter off of that? or a motorcycle battery They are small enough to hang on a belt.
You could certainly use a car or boat battery but then you'd have to charge it as well. That is essentially what those portable power supplies are. A battery with an inverter built in. I don't know if a motorcycle battery would have enough ooomph.
I use the ginormous, old oster clipmasters and a pair of Andis AGC's. Both ran off the inverter with no problem.