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https://electrical-engineering-portal.com/the-real-truth-behind-household-power-savers concludes

Power factor correction devices improve power quality but do not generally improve energy efficiency (meaning they would not reduce your energy bill). There are several reasons why their energy efficiency claims could be exaggerated.

First, residential customers are not charged for KVA – hour usage, but by kilowatt-hour usage. This means that any savings in energy demand will not directly result in lowering a residential user’s utility bill.

yet some reviewers such as on http://amazon.com/dp/B07FSQTBTQ claim that it has saved them money.

What could be the reason? Is it that some electricity meters measure kVA, or that people who want to reduce their bills adopt other measures and incorrectly attribute savings to the device?

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    \$\begingroup\$ Would Electrical Engineering be a better home for this question? \$\endgroup\$ – Qmechanic Jan 12 at 22:24
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    \$\begingroup\$ "What could be the reason?" - Do you believe everything you read on the internet? There are companies which pay people to buy their products and review them. (The review gets the "verified purchase" tag because the reviewer really did "buy it with their own credit card."). Do the math - if you effectively give away 100 products to get 100 5-star reviews, and then sell 10,000 products to people who read those reviews, you still win. \$\endgroup\$ – alephzero Jan 12 at 22:59
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    \$\begingroup\$ Sounds like a gimmick to me. And what do they mean gets rid of carbon? Carbon does not enter through power lines. \$\endgroup\$ – Adrian Howard Jan 12 at 23:51
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    \$\begingroup\$ "some reviewers... claim that it has saved them money" - And some didn't. Top 3 reviews on Amazon:- "We returned the item. Doesn't really do what it says." "No it is not & don't waste your money. My electric bill actually went up." "Wasted money! Lasted 45 days, went out (had 2 of them, both lasted less than 60 days) and I saw no notable savings" \$\endgroup\$ – Bruce Abbott Jan 13 at 20:49
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    \$\begingroup\$ Sounds like a hoax product. However, power factor correction is important in some circumstances. I just don't know whether it is worth going into it in this question. The grid operator can save a bit of energy if customers use power factor correction. Of course it only matters for customers who use a lot of power at low power factor (which does not describe most homes). \$\endgroup\$ – mkeith Jan 13 at 21:28
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Power factor correction uses capacitors to add leading reactive power (VARs or kVARs for large loads) to counter lagging reactive power required by inductive loads like fluorescent lights or motors.

Reactive power goes back and forth between source and load. The capacitors act as a form of battery decreasing reactive power supplied by source.

It does not change the real power W or kW. You pay for energy in kWh. Energy = P t

So power factor correction will benefit the power company, but have no impact on your power bill. Actually, the powers involved are meaningless for homes.

Claims are not reality.

Large consumers require power factor correction if pf is < 0.9, because they pay for kW in kWh, but power companies must provide kVA. Best pf = 1. Companies with a poor pf must pay a surcharge for kWh used.

GreatScott! debunks this. Chinese Power Saver - Does it actually save power? He even mentions claims.

Essentially the device connects a high voltage 2μF capacitor across the mains terminals. Rest of the parts discharge capacitor when disconnected from circuit

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  • \$\begingroup\$ "Rest of the parts discharge capacitor when disconnected from circuit" - I guess we should be thankful for small mercies. \$\endgroup\$ – danmcb Jan 18 at 14:25
  • \$\begingroup\$ @danmcb It is the sketchiest of devices. \$\endgroup\$ – StainlessSteelRat Jan 18 at 15:00

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