Fast charging is a chain. The phone, cable, power adapter, charging standard, battery temperature and current battery level all have to cooperate. If one link is slow, a giant wattage number on the charger box will not fix it.
The fastest way to improve charging is to identify the bottleneck.
The phone decides how much power it can take
A 100W laptop charger does not force 100W into a phone. Compatible devices negotiate power. Apple, for example, specifies particular adapter and cable combinations for iPhone fast charging; current iPhone 17 models can reach roughly 50% in about 20 minutes under Apple’s test conditions with a 40W-or-higher compatible adapter.
The cable can quietly cap the system
Use a cable that supports the connector and power standard required by the phone. A damaged, low-spec or charge-only cable can reduce speed or cause intermittent charging.
Heat makes batteries cautious
Modern phones reduce charging speed when the battery is too warm. Gaming, navigation, video recording or leaving the phone in direct sun while charging can work against the “fast” charger you bought.
Fastest
Screen mostly off, phone cool, compatible wired charger.
Slower
Wireless charging with alignment or heat losses.
Slowest
Heavy use, hot battery, weak adapter or low-power USB port.
Charging intentionally tapers near full
Lithium-ion charging is not a constant-speed fill. Phones reduce power as the battery approaches full, and battery-health features may pause or limit charging based on your settings and routine. Google Pixel, for example, offers charging optimization and an optional 80% limit on supported devices.
Phone capability → charger standard → cable → temperature → battery level
If all five are right, you are probably already close to the device’s intended maximum. At that point, buying an even larger adapter is usually a victory for the accessory drawer, not the battery meter.