To start with, welcome to the Gauge. I would not think you have a power pack problem rather, it is more likely that your locos need cleaning. You don't say what scale they are or if they're steam or diesel. But, it you do a search here at the Gauge, you can find several discussions regarding cleaning and lubercating engines. After that long in the attic, you can be sure they have collected a lot of dust and the oil has dried out. I wouldn't try to run them any more until they have been cleaned and lubed.
Basically you will need to remove the shells and use a mild cleaning solution, like soap and water or alcohol. Don't use solvents like acetone or laquer thinner. Use a very light oil, very sparingly to lub the moving parts. Make sure the motor turns freely as well, and be sure the wheels are clean so you get good electrical contact with the rails.
A few years ago, I bought a collection of N scale that included around 30 engines that were sitting on a layout in a garage untouched for at least ten years. They all were in serious need of cleaning. I wound up putting some of the engines in an ultrasonic cleaner and a few I never did get to run right.
Good luck