An AC charger converts wall power into the right voltage and current for your device
An AC charger is the brick or cable you plug into a wall outlet to charge your phone, laptop, tablet, or other portable device. The "AC" stands for alternating current — the type of electricity that comes out of your wall. The charger's job is to take that wall power and convert it into direct current (DC) at the exact voltage your device needs, then deliver it safely through a cable or connector.
Most AC chargers have two parts: a power adapter (the brick) that does the conversion, and a cable with a connector that plugs into your device. Some newer chargers combine both into a single unit. Without a charger, your device's battery cannot draw power from the wall, so the charger is what actually makes charging possible.
Key Takeaways
- An AC charger converts wall outlet electricity into the lower voltage your device needs to charge safely.
- The power adapter (brick) does the conversion work, while the cable delivers power to your device.
- Different devices need different voltages and connector types, which is why chargers are not interchangeable.
- Damaged chargers can overheat, fail to charge, or damage your device's battery, so replacement is usually necessary.
How the conversion from AC to DC actually works
Wall outlets supply alternating current at around 120 volts (in North America) or 230 volts (in Europe and most other regions). Your phone or laptop battery, by contrast, runs on direct current at much lower voltages — typically 5 to 20 volts depending on the device.
The power adapter contains a transformer that steps down the voltage, then a rectifier that converts the alternating current to direct current. Finally, a regulator ensures the output stays at exactly the right voltage so your device charges without damage. All of this happens inside the brick, which is why it gets warm during charging — the conversion process generates heat as a byproduct.
Why different devices need different chargers
A charger for your phone will not work for your laptop, and a tablet charger may not work for either, because devices have different power requirements. A phone typically needs 5 volts, while a laptop might need 20 volts or more. The connector shape also differs — USB-C, Lightning, micro-USB, and proprietary connectors all look different and fit different ports.
Using the wrong charger can damage your device's battery or charging circuit. A charger that supplies too much voltage can overheat the battery or cause it to fail. A charger that supplies too little voltage may not charge at all, or charge so slowly that it seems broken. Always check your device's manual or the label on the original charger to see what voltage and connector type it needs.
Common types of AC chargers you will encounter
USB chargers are the most common type for phones and small devices. They output 5 volts and use a USB connector (standard USB-A, USB-C, or micro-USB). These are simple and inexpensive, and many devices share the same standard.
Laptop chargers are larger and heavier because laptops draw more power. They typically output 15 to 20 volts and use a barrel connector or USB-C. Some newer laptops charge via USB-C, which means you can use a high-power USB-C charger instead of a proprietary one.
Fast chargers output higher wattage to charge devices more quickly. They still output the same voltage as standard chargers but deliver more current, so the battery fills faster. Your device must support fast charging for this to work — using a fast charger on a device that does not support it will not harm anything, but it will not charge any faster.
What to do if your charger stops working
A charger that no longer charges your device may have a damaged cable, a failed power adapter, or a loose connection. Start by checking the cable for visible damage — bent connectors, frayed wires, or cracks in the insulation are signs of failure. If the cable looks fine, try a different outlet to rule out a tripped breaker or dead outlet.
If the charger still does not work, the power adapter itself has likely failed. The safest option is to replace it with a new charger of the same type and voltage. Do not attempt to repair a damaged charger by taping it or wrapping it — a broken charger can overheat and pose a fire risk. Buy a replacement from the device manufacturer or a reputable third-party maker that lists your device model on the packaging.
How to tell if a charger is the right one for your device
Check three things before you use a charger: the voltage, the connector type, and the wattage. The voltage is printed on a label on the power adapter itself — it looks like "5V" or "19V" or "20V". Your device's manual or the original charger will tell you what voltage you need. The connector must physically fit your device's charging port without forcing it.
The wattage (measured in watts, or W) tells you how much power the charger can deliver. A charger with higher wattage than your device needs is safe to use — it will simply deliver what your device asks for. A charger with lower wattage may charge slowly or not at all. If you are unsure, match the wattage of your original charger as closely as possible.
Frequently Asked Questions
Can I use a phone charger to charge my tablet?
Only if the tablet's charging port matches the phone charger's connector and the voltage is the same. Most tablets need higher voltage than phones, so a phone charger will either not fit or will charge very slowly. Check your tablet's manual before trying.
Why does my charger get hot?
Chargers generate heat during the conversion from AC to DC — this is normal. However, if the charger is too hot to touch or smells like burning plastic, unplug it immediately. Excessive heat means the charger is failing and should be replaced.
Is it safe to leave a charger plugged in all the time?
Modern chargers are designed to be left plugged in without damage. Once your device is fully charged, the charger stops delivering power. However, unplugging chargers when not in use saves a small amount of electricity and reduces wear over time.
What is the difference between USB-C and other USB chargers?
USB-C is a newer connector standard that is smaller, reversible (it works either way you plug it in), and can deliver higher power than older USB types. Many newer phones and laptops use USB-C, but older devices use micro-USB or proprietary connectors. The charger must match your device's port.
Can a charger damage my device's battery?
Using the wrong charger — one with incorrect voltage or wattage — can damage your battery or charging circuit. Using the correct charger will not damage your battery, even if you charge overnight. Modern devices have built-in protection that stops charging once the battery is full.