Best 24 Volt Power Supply for Thermostat: Top 7 Picks (October 2026)

The best 24 volt thermostat power supplies include the BOJACK 24V 40VA Thermostat and Doorbell Transformer for a wired thermostat replacement, the LIANSUM 24V Transformer C Wire Adapter for a long plug-in cable, and the CENTROPOWER Plug-in Doorbell Power Supply for plug-in 24 V AC power.

On this page (6 sections)

1. Which 24 volt thermostat power supplies made the cut?
2. What should you check before choosing a 24 volt transformer for a thermostat?
3. Which 24 volt power supply for thermostat setups is best?
4. Can a 24 V DC adapter power an HVAC thermostat?
5. When is a plug-in thermostat power supply a good fit?
6. How do you choose the best 24 volt power supply for thermostat use?

The best 24 volt power supply for a thermostat is usually a 24 V AC transformer matched to the thermostat's power needs. The BOJACK 24V 40VA Thermostat and Doorbell Transformer is our top pick here, while the LIANSUM offers a plug-in option with a long cable.

These options aren't interchangeable. Several are 24 V DC adapters designed for general electronics, while HVAC thermostat circuits commonly call for 24 V AC.

Check the thermostat manual, existing transformer label and terminal diagram before you buy.

If your thermostat needs power because there is no C wire, first see whether an adapter or power extender kit fits your system. Our guides explain what a power extender kit does and what a Nest Power Connector is.

For other low-voltage adapter choices, compare our Best C Wire Adapter For No C Wire Setups.

Which 24 volt thermostat power supplies made the cut?

These picks are ranked by their site-wide scores, with the BOJACK first at 9.7. We compared the output type, voltage, capacity, connection style and stated compatibility, while treating DC-only adapters as choices for equipment that specifically accepts DC.

Our score weighs specs and features against what you're shopping for. Match your thermostat's requirements to the supply before choosing.

Our picks at a glance

1. 1
   Best for a wired thermostat replacement

   BOJACK 24V 40VA Thermostat and Doorbell Transformer

   9.7/10 our score

   See it on Amazon
2. 2
   Best for a long plug-in cable

   LIANSUM 24V Transformer C Wire Adapter

   9.6/10 our score

   See it on Amazon
3. 3
   Best for plug-in 24 V AC power

   CENTROPOWER Plug-in Doorbell Power Supply

   9.0/10 our score

   See it on Amazon

4. 4

   OhmKat Professional Grade Short Protected 24 Volt

   Best for a dedicated thermostat supply
   Check it
5. 5

   YOOFONE 24V Power Supply 24V 5A Power

   Best for compatible DC equipment
   Check it
6. 6

   Meiyue 24 Volt 6 Amp Power Supply

   Best for a 24 V DC terminal option
   Check it
7. 7

   VAYALT 24V 25A 600W DC Switching Power

   Best for multi-device DC projects
   Check it

What should you check before choosing a 24 volt transformer for a thermostat?

Check AC or DC output first, then match voltage, current or VA, wiring method and device compatibility. A 24 V label alone doesn't confirm that a supply will work with an HVAC thermostat.

• Output type: The BOJACK, LIANSUM and CENTROPOWER provide 24 V AC. YOOFONE, Meiyue and VAYALT provide 24 V DC; OhmKat's output type isn't specified.
• Capacity: Compare the thermostat's requirements with the transformer's current or VA rating. Don't assume a higher capacity DC supply can replace a 24 V AC transformer.
• Connections: Check whether the thermostat needs screw terminals, two low-voltage leads or a specific adapter connector.
• Compatibility: Match the exact thermostat model and generation. LIANSUM states compatibility with Nest 1st and 2nd generation, but not 3rd generation.
• Power source and wiring: A plug-in supply and a transformer mounted at an electrical box involve different installation needs.

If you're considering an external supply with a Nest, read how to install a smart thermostat with a dual transformer system before connecting separate power sources. A wiring mistake can damage equipment.

Which 24 volt power supply for thermostat setups is best?

The BOJACK is the highest-scoring pick and a fit for a wired replacement where 24 V AC at 40 VA meets the system's needs. Other options include plug-in supplies, a long-lead 24 V supply, and DC adapters for compatible equipment.

1

BOJACK 24V 40VA Thermostat and Doorbell Transformer: Best for a wired thermostat replacement

9.7/10Our score

• 24 V AC output
• 40 VA
• 120 V AC input
• Screw-down and thread clamps

A 24 V AC, 40 VA transformer aimed at thermostat and doorbell use. It fits buyers replacing an underpowered transformer who can connect it to an electrical box.

See it on Amazon

Pros

• 24 V AC output
• 40 VA capacity
• Thermostat compatibility includes Nest, Ecobee, Sensi and Honeywell

Cons

• Electrical box wiring may not suit every setup
• Confirm the thermostat's power requirements before connecting

The BOJACK transformer provides 24 V AC at 40 VA from a 120 V AC input. Its stated thermostat compatibility includes Nest, Ecobee, Sensi and Honeywell.

Its screw-down and thread clamps connect to an electrical box. That can suit a replacement where the existing transformer is mounted near the HVAC equipment, but it may not fit a setup that needs a plug-in adapter.

BOJACK also names compatibility with several Ring doorbells. If the transformer will power more than one device, compare the combined load with its 40 VA rating and each device's requirements.

Choose it when you need a wired 24 V AC transformer and have confirmed the installation and load match your system. For a missing C wire, see our Best Power Extender Kit For Smart Thermostats guide.

2

LIANSUM 24V Transformer C Wire Adapter: Best for a long plug-in cable

9.6/10Our score

• 24 V AC output
• 500 mA output
• 8 m cable
• Two non-polarity wires

The 8 m cable can reach from an outlet to a thermostat, and the adapter provides 24 V AC at 500 mA. Check model compatibility, especially the stated Nest generation limit.

See it on Amazon

Pros

• Long 8 m cable
• Non-polarity wire connections
• Plug-in power source

Cons

• Not compatible with Nest 3rd generation
• 500 mA output may not suit every thermostat

LIANSUM suits a thermostat setup where a long wire run from an outlet is useful. Its 8 m cable ends in two non-polarity wires, and its stated output is 24 V AC at 500 mA.

Model compatibility needs care. LIANSUM names Nest 1st and 2nd generation, Ecobee, Honeywell and Sensi, but excludes Nest 3rd generation.

LIANSUM's instructions describe connecting the adapter leads to the thermostat's C and RC terminals. They also mention an included diode for some cooling systems, so follow the instructions for your exact thermostat and HVAC system.

Choose it if your thermostat supports this external adapter method and 500 mA meets its requirements. Skip it if you need more current or have a Nest 3rd generation thermostat.

3

CENTROPOWER Plug-in Doorbell Power Supply: Best for plug-in 24 V AC power

9.0/10Our score

• 24 V AC output
• 1.6 A total output current
• Screw terminals
• Green power indicator

This plug-in transformer supplies 24 V AC and uses screw terminals for the low-voltage connection. It suits buyers who want an outlet-powered option with a green power indicator.

See it on Amazon

Pros

• 24 V AC output
• Plug-in installation
• Green power indicator

Cons

• Confirm compatibility with your specific thermostat
• Keep the outlet and cable route accessible

CENTROPOWER is a plug-in choice with 24 V AC output at 1.6 A and screw terminals for the low-voltage connection. It has a green power indicator, and its stated compatibility includes Nest, Ecobee, Sensi and Honeywell thermostats.

Its stated current is higher than LIANSUM's 500 mA, but that alone doesn't guarantee compatibility with every thermostat. Check your model's requirements and whether it supports a separate plug-in transformer.

Choose it if you want an outlet-powered 24 V AC supply with screw terminals. Check that the outlet and wire route can reach the thermostat safely.

4

OhmKat Professional Grade Short Protected 24 Volt: Best for a dedicated thermostat supply

8.4/10Our score

• 24 V output
• Short-circuit protection
• 30 ft wire
• Barrel jack or screw terminal

The 30 ft wire and short-circuit protection make this a focused option for C-wire and 24 V applications. Check whether its connection style and 24 W output match your thermostat.

See it on Amazon

Pros

• Short-circuit protection
• 30 ft wire
• Barrel jack or screw terminal

Cons

• Output type is not specified as AC or DC
• Confirm the thermostat's required current and connection

OhmKat is designed for C-wire and 24 V applications, including smart thermostats and sprinkler controllers. Its 30 ft wire and short-circuit protection may help when the power source needs to sit away from the thermostat.

Its output is 24 V and 24 W, but the output type isn't specified. Confirm that point with OhmKat, and compare the barrel jack or screw terminal connection options with your equipment.

The supply also has a one-touch power test. Consider it only after confirming that its output type, capacity and wiring method match your thermostat.

5

YOOFONE 24V Power Supply 24V 5A Power: Best for compatible DC equipment

9.4/10Our score

• 24 V DC output
• 5 A maximum
• 120 W maximum
• 5.5 mm barrel connector

This adapter supplies 24 V DC through a barrel connector, a different format from the 24 V AC transformers commonly used in thermostat wiring. Consider it only when your equipment specifically accepts its DC output and connector.

See it on Amazon

Pros

• 24 V DC output
• Up to 5 A
• Overload, overvoltage, overcurrent, overheating and short-circuit protections

Cons

• DC output may not match an AC thermostat input
• Barrel connector may not fit thermostat terminals

YOOFONE is a 24 V DC adapter for equipment with a matching barrel connector. It supplies up to 5 A and 120 W, with a 5.5 mm outer connector and a stated inner diameter of 2.1 to 2.5 mm.

The adapter has overload, overvoltage, overcurrent, overheating and short-circuit protection. YOOFONE specifies positive polarity inside and negative outside, so the connected device must accept that polarity.

Choose it only if your equipment explicitly accepts 24 V DC through a compatible barrel jack. Its higher current rating doesn't make it suitable for AC thermostat terminals.

6

Meiyue 24 Volt 6 Amp Power Supply: Best for a 24 V DC terminal option

9.2/10Our score

• 24 V DC output
• 6 A maximum
• 144 W maximum
• LED terminal connector included

The 24 V DC supply includes an LED terminal connector for screw-wire connections. Its DC output and higher current capacity make it a fit only for compatible equipment, not a default choice for thermostat terminals.

See it on Amazon

Pros

• 24 V DC output
• LED terminal connector included
• 100–240 V AC input

Cons

• DC output may not match an AC thermostat input
• Confirm plug size and polarity for your equipment

Meiyue supplies 24 V DC at up to 6 A and 144 W, with a 5.5 x 2.5 mm output jack and an included LED terminal connector. It can serve compatible DC equipment that needs screw-wire connections or a matching barrel jack.

Its stated protections include overload, overvoltage, overcurrent, overheating and short circuit. Check the connector size and positive-inside polarity against your device before connecting it.

This is a DC supply, so it won't replace a 24 V AC transformer unless your equipment accepts DC input. Its extra current capacity is useful only when the connected device needs it.

7

VAYALT 24V 25A 600W DC Switching Power: Best for multi-device DC projects

8.7/10Our score

• 24 V DC output
• 25 A maximum
• 600 W maximum
• Adjustable output voltage

This high-capacity switching supply is designed for 24 V DC equipment and projects. Its exposed terminals, fan and large power capacity make it a poor default fit for a simple thermostat replacement.

See it on Amazon

Pros

• 24 V DC output
• Adjustable output voltage
• Overload, overcurrent and short-circuit protection

Cons

• DC output may not match an AC thermostat input
• Large capacity and exposed terminals need careful installation

VAYALT is a high-capacity 24 V DC switching supply for equipment and projects that need up to 25 A or 600 W. It has adjustable output voltage, a temperature-controlled fan, and overload, overcurrent and short-circuit protections.

This supply has an aluminum alloy casing and terminals for power connections. Its product instructions advise matching the supply to the equipment's power needs and avoiding extended overload.

Choose it for compatible DC projects, not as a default thermostat supply. Confirm that your equipment accepts 24 V DC and that the installation suits this type of supply.

Can a 24 V DC adapter power an HVAC thermostat?

A 24 V DC adapter can power a thermostat only when that thermostat explicitly accepts DC at the required current and connection type. Many HVAC systems use 24 V AC control circuits, so a DC supply may be incompatible.

YOOFONE, Meiyue and VAYALT provide DC output. Their current ratings don't compensate for a mismatch in output type.

If you want to avoid external wiring, a thermostat with battery power may be another option. See our guide to the Best Smart Thermostat With Battery Power.

When is a plug-in thermostat power supply a good fit?

A plug-in transformer can suit a thermostat that supports an external 24 V AC source and can be reached from a nearby outlet. LIANSUM and CENTROPOWER are the plug-in AC options in this group.

Before buying, confirm that the thermostat supports separate power, the cable reaches safely and the output meets the device's requirements. Don't connect a new supply to existing R and C wiring until you understand how your HVAC system is configured.

How do you choose the best 24 volt power supply for thermostat use?

Choose BOJACK for a wired 24 V AC, 40 VA transformer replacement when that rating suits your system. Consider LIANSUM for a long plug-in cable and CENTROPOWER for a plug-in AC supply with a higher stated current; check OhmKat's output type before considering it.

Choose YOOFONE, Meiyue or VAYALT only if your equipment accepts 24 V DC. Match the output, capacity, connection and wiring diagram before connecting power, and get qualified help if the system uses two transformers or the wiring is unclear.

Our top 3 picks at a glance

1. 1
   Best for a wired thermostat replacement

   BOJACK 24V 40VA Thermostat and Doorbell Transformer

   9.7/10 our score

   See it on Amazon
2. 2
   Best for a long plug-in cable

   LIANSUM 24V Transformer C Wire Adapter

   9.6/10 our score

   See it on Amazon
3. 3
   Best for plug-in 24 V AC power

   CENTROPOWER Plug-in Doorbell Power Supply

   9.0/10 our score

   See it on Amazon

Frequently asked questions

Can I use any 24 volt power supply for a thermostat?

No. Match the thermostat's required output type, voltage, current or VA, and connection method.

Many HVAC thermostats use 24 V AC, while several general-purpose adapters here supply 24 V DC.

Check the thermostat wiring diagram and the existing transformer label before choosing a replacement.

What does 40 VA mean on a 24 volt transformer?

40 VA describes the transformer's apparent power capacity, rather than its output current by itself. At 24 V, a 40 VA transformer can provide about 1.67 A under its rated conditions.

Compare the thermostat and any other connected equipment's requirements with the transformer's rating.

Can I use a 24 volt DC adapter with a thermostat?

Only if the thermostat explicitly accepts 24 V DC and its connector matches the adapter. A DC power supply is not interchangeable with a 24 V AC HVAC transformer just because both are labeled 24 V.

Check polarity and the wiring diagram before connecting any DC adapter.

Can a plug-in transformer add a C wire?

A compatible plug-in 24 V AC transformer can provide a separate power source for some thermostat setups, but the wiring method depends on the thermostat and HVAC system. Confirm whether the thermostat supports an external transformer and how its C and R terminals should be connected.

For system-specific wiring, consult the thermostat instructions or an HVAC professional.

Should I replace a thermostat transformer myself?

Only work on wiring you can identify and safely isolate. A transformer connected to household voltage can present a shock hazard, and a dual-transformer HVAC system needs careful wiring so the power sources are handled correctly.

Turn off the relevant circuit and get qualified help if the wiring or transformer rating is unclear.