Yes. Some electrolytic capacitors may be shorted, even if the amp is idle for as little as six months, depending how old they are. What happens is that a thin layer of aluminum oxide insulating the foil deteriorates and the cap shorts out. This insulating layer can be reformed by applying a low voltage across the cap in increments up to its rated voltage.
The best way to do it is to call the manufacturer and ask what should be done if the amp was idle for more than a few months (or whatever time frame you're concerned with). The other thing that can be done is to plug the amp into a variac, start at 10 volts and work up to the wall voltage (120, 240, etc) in 10 volt increments each hour. This is FYI - I am not assuring that no damage would occur to any particular amp because there's no telling if the cap reformed. You can only know this by using certain commercial test instruments (an easily home-made one works) or hope for the best by not hearing a bang. But as always, ask the mfr before you try anything like this.
