Quick answer: a replacement laptop charger is compatible when three things match: the output voltage is the same as the original, the wattage is equal to or higher than the original, and the connector (barrel size or USB-C) fits your laptop. All three are printed on the label of your original adapter.
1. Voltage must match
The output voltage (marked "OUTPUT" on the adapter label, for example 19.5V) must be the same as the original. A different voltage can fail to charge or damage the laptop. Within a brand, voltage is usually consistent: most Dell and HP barrel chargers output 19.5V, most Lenovo chargers 20V, and many ASUS and Acer chargers 19V. Always confirm on your own label.
2. Wattage: equal or higher
Wattage is the maximum power the charger can supply. A higher-wattage charger with the same voltage and connector is safe, because the laptop only draws what it needs. A lower-wattage charger may charge slowly, stop charging under load, or trigger a warning at startup. Gaming laptops often need 180W to 330W; thin-and-light laptops typically 45W to 65W.
3. The connector
Barrel connectors are described by outer and inner diameter in millimeters. Common sizes by brand:
| Brand | Typical voltage | Common connectors |
|---|---|---|
| Dell | 19.5V | 4.5 × 3.0 mm (newer models), 7.4 × 5.0 mm (older and higher-wattage), USB-C on recent XPS and Latitude |
| HP | 19.5V | 4.5 × 3.0 mm (blue tip), 7.4 × 5.0 mm, USB-C on recent EliteBook, Spectre and Envy |
| Lenovo | 20V | Rectangular "slim tip", older round 7.9 × 5.5 mm, 4.0 × 1.7 mm on some IdeaPads, USB-C on recent ThinkPads |
| ASUS | 19V or 20V | 4.0 × 1.35 mm on many VivoBook and ZenBook models, 5.5 × 2.5 mm on older models, larger tips on ROG gaming laptops, USB-C |
| Acer | 19V | 5.5 × 1.7 mm on many Aspire and Nitro models, 3.0 × 1.1 mm on some Swift and Spin models, USB-C |
| Microsoft Surface | 15V | Surface Connect magnetic connector, USB-C on newer models |
| Apple MacBook | Varies | MagSafe 1 or 2 (older), MagSafe 3 or USB-C Power Delivery (2021 and later) |
These are typical values, not a guarantee for every model. Dell and HP also use a center "smart pin" on many chargers so the laptop can identify the adapter; a charger without a working ID pin may charge slowly or show a warning.
USB-C laptops
If your laptop charges over USB-C, look for a USB-C Power Delivery (PD) charger with at least the wattage of the original. Use a cable rated for the wattage too: cables rated for 60W are common, and chargers above 60W need a 100W or 240W rated cable to deliver full power.
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Replacing a worn battery as well? See Dell, HP and Lenovo laptop batteries, or all laptop chargers and power adapters.
Frequently asked questions
Can I use a higher-wattage charger?
Yes, as long as the voltage and connector match. The laptop only draws the power it needs.
Why does my laptop say "unknown adapter"?
On many Dell and HP laptops this means the charger's ID pin is not being read, often because of a damaged cable or tip, or a charger without the ID chip. The laptop may limit charging until a recognized adapter is connected.
Where do I find my charger's specs?
On the label of the original adapter: look for OUTPUT (volts and amps) and the wattage. Multiply volts by amps if wattage is not printed, for example 19.5V × 3.34A ≈ 65W.