For years, the quest for the fastest possible charge has been a key battleground for smartphone users. With the release of the iPhone 17, Apple continues to support USB-C Power Delivery (PD), but a new, optional 40W charger has sparked a debate: does it offer a significant charging advantage, or is it just marketing? To find the definitive answer, the expert testers at ChargerLAB put the iPhone 17 through a rigorous charging analysis, pitting four of Apple's own power adapters against each other.
The test was designed to eliminate variables and deliver real-world results. Using a high-precision POWER-Z KM003C tester and POWER-Z Lab V2.4 software inside a controlled 25 °C (77 °F) thermotank, they meticulously tracked the iPhone 17's power draw and charging times with the 20W, 40W, 70W, and 140W USB-C adapters. The results were surprising, to say the least.
The Baseline: Charging with the 20W Adapter
Starting with the popular and affordable 20W adapter, the iPhone 17 behaved as expected for a standard PD charge. It triggered a 9V output and drew a peak of 19W. This power level was maintained for the first 36 minutes before beginning a steady decline, dropping to 12W and then to around 7W by the 65-minute mark as it entered the final trickle-charging phase. The phone reached:
- 50% charge in 27 minutes
- 80% charge in 52 minutes
- 100% full charge in 1 hour and 50 minutes
This provides a solid baseline for what most users would consider a "fast" charging experience.
Stepping Up: The 40W, 70W, and 140W Adapters
This is where the data gets fascinating. When the testers switched to the more powerful adapters, the iPhone 17 consistently triggered a higher 15V output.
With the 40W Adapter: The phone peaked at an impressive 36W and held a robust 28W for the first 11 minutes. The power then gradually declined in a step-like pattern, eventually settling to about 8W by the 57-minute mark. The final charging times were:
- 50% in 19 minutes
- 80% in 44 minutes
- 100% in 1 hour and 42 minutes
With the 70W Adapter: The performance was nearly identical, with a slightly higher peak of 36.7W. It held the 28W level for a bit longer—13 minutes—before stepping down through 24W, 19W, and 12W. Despite the higher wattage potential, the final times were virtually the same:
- 50% in 19 minutes
- 80% in 44 minutes
- 100% in 1 hour and 42 minutes
With the 140W Adapter: The story repeated itself. Even with this powerhouse adapter—designed for a 16-inch MacBook Pro—the iPhone 17 peaked at around 36W. The charging curve was almost a carbon copy of the others, resulting in:
- 50% in 18 minutes
- 80% in 42 minutes
- 100% in 1 hour and 41 minutes
For a more visual breakdown of how these charging curves compare side-by-side, the team at ChargerLAB has published a detailed video.
The Verdict: Bigger Isn't Always Better
When all the data is plotted on a single graph, the conclusion is inescapable: the charging curves for the 40W, 70W, and 140W adapters are almost identical. Averaging the results shows the iPhone 17 reaching 50% in about 19 minutes, 70% in 30 minutes, 80% in 41 minutes, and a full charge in approximately 1 hour and 39 minutes.
While all the larger adapters are significantly faster than the 20W brick, the differences between them are minimal. The 70W adapter might shave a single minute off the total charging time, but it's a negligible gain for the average user.
According to ChargerLAB's analysis, this proves a critical point: the iPhone 17's charging circuitry is still governed by the standard USB-C Power Delivery (PD) protocol. Despite speculation that Apple's new 40W charger, which features the SPR AVS protocol, would unlock special "fast charge" capabilities, the data shows no such advantage. The phone simply will not draw more than approximately 36-37W, regardless of the adapter's maximum output.
The Bottom Line for iPhone 17 Owners
So, what does this mean for you? If you already own a 20W Apple adapter, you're getting a good charging experience. However, upgrading to a higher-wattage adapter will get you to a 50% charge about 8-9 minutes faster, which can be a lifesaver when you're in a rush.
The key takeaway is that you don't need to splurge on the most expensive option. For the fastest possible charge on the iPhone 17, any quality USB-C PD adapter rated at 30W or above will essentially perform the same as the 140W model. The new 40W adapter offers no special secret sauce, making your choice a simple matter of price and preference.