For situations where a UPS is too expensive or impractical you can also buy pure voltage regulators that use some kind of autotransformer, like the APC Line-R. I worked for an institution for a while that had every laser printer on one, there had been some bad experiences with losing laser printers to overvoltage incidents but they generally draw too much current to go on a UPS. I've also seen them used for A/V equipment.