The Wild West of USB Charging: How We Got From 2.5 Watts to Today
USB charging started at 2.5 watts. How USB Battery Charging, Apple's amperage hack, and Qualcomm's voltage boost led to the modern USB-C standard.
Before Power Delivery, before USB-C, before your laptop could pull 90 watts off a single cable, charging over USB was a mess. This is the story of how it got that way, and how it got fixed - starting with the oldest charging idea there is: USB Battery Charging mode.
It started at 2.5 watts
When USB first arrived, it wasn’t built to charge anything. It was a data port that happened to carry a little power on the side - 5 volts at half an amp. That’s 2.5 watts. Enough to sip power into a device while it synced, and nowhere near enough to charge a phone at any speed you’d tolerate.
As phones got hungrier, 2.5 watts became a joke. And the official standard wasn’t moving fast enough. So companies stopped waiting.
The Wild West
With no fast standard to follow, everyone hacked their own. Two camps formed, and they went in opposite directions.
Apple cranked up the amperage. By signaling on the data pins, Apple’s chargers told Apple devices they could safely pull more current - 2.1 amps, then 2.4 amps at 5 volts. That’s how the famous 10-watt and 12-watt iPad bricks were born: same 5 volts, just more amps.
Samsung and Qualcomm cranked up the voltage. Qualcomm’s Quick Charge and Samsung’s Adaptive Fast Charging pushed the voltage up to 9 or 12 volts instead, delivering more power without needing thick, high-current cables.
Both worked. Neither talked to the other. A Qualcomm charger did nothing special for an iPhone, and an Apple charger did nothing special for a Galaxy. Buy the wrong brick and you got slow, standard charging with no explanation.
The 7.5-watt speed limit
Here’s the thing all these hacks were quietly getting around. The official USB group did eventually publish a charging spec - USB Battery Charging 1.2 (BC 1.2) - and it capped a standard USB-A port at 7.5 watts: 5 volts at 1.5 amps.
So any charger pushing past 7.5 watts on USB-A - every Apple 10 and 12-watt brick, every Quick Charge charger - was, technically, off-spec. It worked because the charger and the device had a private handshake the standard didn’t define. It was fast, but it was the Wild West, and it couldn’t last.
Apple changed sides
Apple saw where this was going and got involved in shaping the next connector: USB-C. It was one of the first companies to ship it, putting a lone USB-C port on the 2015 MacBook years before the rest of the industry caught up.
But sitting at that table came with a decision that still affects your charging today: going forward, Apple’s Macs and iPhones would honor true-spec USB charging and drop the old proprietary tricks. No more private handshakes. If it wasn’t in the standard, the device wouldn’t use it.
The irony: Apple crippled its own charger
Which leads to a genuinely strange result. Plug that old, iconic Apple 12-watt brick into a modern Mac, and the Mac refuses the old 2.4-amp trick. It falls back to plain BC 1.2 and caps at that same 7.5 watts. We measured it: the 12-watt charger delivers about 7 watts to a MacBook, identical to the 10-watt one. Apple effectively disabled its own famous charger to enforce the standard it helped write.
But here’s the twist that makes it interesting: a modern iPhone does the opposite. Plug that same 12-watt brick into a current USB-C iPhone and it still pulls the full 12 watts. The iPhone kept support for the old signaling; the Mac gave it up. Same charger, same era of hardware, and the two Apple devices treat it completely differently - the phone honors the past, the laptop enforces the future.
A small price to pay to shape the future of charging? Apple clearly thought so.
What came next
Everything since has been built on the standard instead of around it. USB Power Delivery replaced the Wild West with a real negotiation: first a menu of fixed voltage steps - 5, 9, 15, 20 volts - and later sliding, adjustable ranges that dial the voltage in precisely.
That’s how a single USB-C cable went from 2.5 watts to 240. But that’s a story for another day.
If you want to see which of these your own charger is actually using - the old battery-charging fallback, a fixed PD step, or a modern adjustable range - USB Connection Information shows it the moment you plug in.