OK - There are at least 3 different things at work here:
1: The input voltage and current available to your amp from the wall socket. As others have pointed out, there's pretty much nothing you can do about this. It also doesn't likely matter much - firstly because you can't fix it, and secondly because it won't affect the output very much.
2: Gain structure. The idea here is to set your equipment so that you have access to all of the power your amp can deliver (if you need it), but also aren't using too much gain (amplification - either at your power amp or at some preamp stage inside your mixer or crossover) so that you get hiss.
3: Setting limiters to prevent clipping and reduce the chance of speaker damage.
I don't see at least in this thread what equipment you are using. Please tell us which amps, what speakers, and if you have any kind of crossover or other processor in the middle. This will help.
Read up on gain structure both by searching on the forum, and by reading stuff here:
http://www.rane.com/library.htmlAlso check out how limiters work.
One piece of good advice that you have received is to "have enough rig for the gig". There are 2 ways to look at this - either lower your expectations to what the gear you currently own can handle, or get a bigger system.
Sound pressure and electrical power are not linear in this context. After you get up a ways into the output of your speakers, it takes a lot more electrical power to make a small sound pressure difference. This large electrical power difference also determines whether your speakers are humming along comfortably, or being pushed to the limit. This is why Ivan and others are saying to not sweat the last little bit - even leaving 10% or 20% of your amp unused (if that's happening - I expect it's not), that only equals 1 or 2 dB of less output.
After you get the concepts sorted out you'll know where to go. And don't feel bad about buying the meter - you'll use it plenty going forward. I never bring gear without one.