How to Choose a Laptop Charger

Start with the label on your original adapter or your laptop's spec sheet. It lists an output voltage (for example 19.5V or 20V) and a wattage (45W, 65W, 90W, 140W and up). Voltage must match exactly - a 19.5V laptop should not be fed 20V from a mismatched supply. Wattage you can match or exceed, because a laptop only draws what it needs, but you must never go under: an undersized charger charges slowly, drains the battery under heavy load, or refuses to charge.

Then confirm the connector. Modern ultrabooks and MacBooks charge over USB-C Power Delivery (PD), where voltage is negotiated automatically, so any certified PD charger of the right wattage will work. Older laptops, and most gaming and workstation machines, use round barrel plugs or proprietary connectors - and barrel sizes are not universal, so the outer and inner diameter and the polarity have to match your model, not just look similar.