A power conditioner (also known as a line conditioner or power line conditioner) is a device intended to improve the quality of the power that is delivered to electrical load equipment. The term most often refers to a device that acts in one or more ways to deliver a voltage of the proper level and characteristics to enable load equipment to function properly. In some uses, power conditioner refers to a voltage regulator with at least one other function to improve power quality (e.g. power factor correction, noise suppression, transient impulse protection, etc.)

Conditioners specifically work to smooth the sinusoidal A.C. wave form and maintain a constant voltage over varying loads.

An AC power conditioner is the typical power conditioner that provides "clean" AC power to sensitive electrical equipment. Usually this is used for home or office applications and commonly provides surge protection as well as noise filtering.

Power line conditioners take in power and modify it based on the requirements of the machinery to which they are connected. Attributes to be conditioned are measured with various devices. Voltage spikes are most common during electrical storms or malfunctions in the main power lines. The surge protector stops the flow of electricity from reaching a machine by shutting off the power source.

A good quality power conditioner is designed with internal filter banks to isolate the individual power outlets or receptacles on the power conditioner. This eliminates interference or "cross-talk" between components. For example, if the application will be a home theater system, the noise suppression rating listed in the technical specifications of the power conditioner will be very important.^{[citation needed]} This rating is expressed in decibels (db). The higher the db rating, the better the noise suppression.

Active power filters (APF) are filters which can perform the job of harmonic elimination. Active power filters can be used to filter out harmonics in the power system which are significantly below the switching frequency of the filter. The active power filters are used to filter out both higher and lower order harmonics in the power system.

The main difference between active power filters and passive power filters is that APFs mitigate harmonics by injecting active power with the same frequency but with reverse phase to cancel that harmonic, where passive power filters use combinations of resistors (R), inductors (L) and capacitors (C) and do not require an external power source or active components such as transistors. This difference makes it possible for APFs to mitigate a wide range of harmonics.

The power conditioner will also have a "joule" rating. A joule is a measurement of energy or heat required to sustain one watt for one second, known as a watt second. Since electrical surges are momentary spikes, the joule rating indicates how much electrical energy the suppressor can absorb at once before becoming damaged itself. The higher the joule rating, the greater the protection.