Those power conditioners are great.
Low voltage at some venues is not uncommon. Low enough and it will affect how your amp sounds and the bias setting of a tube amp.
I use a heavy duty construction, 12 gauge, 50 foot extension cord that I got from Home Depot to get the power to the amp. You can typically find them in 50 and 100 foot lengths. Power strips can have issues.
While at a hardware store, buy one of those LED outlet testers for a couple a bucks. It will tell you if your outlet is wired properly so that you can ensure that you have a safe ground before plugging in.
Official Ampeg Portaflex Club #89