Power Banks and Fast Charging Explained: Watts, PD, GaN

 

By Sidra Salman · November 6, 2026

Last month I stood in an electronics aisle staring at a wall of chargers and power banks, and I realized something embarrassing: I write about gadgets for a living, and even I couldn't tell at a glance which of these bricks would actually charge my laptop. One box shouted "240W!" Another said "GaN II" like it was a movie sequel. A power bank promised 20,000mAh — a number it will never actually deliver to your phone.

So I spent the last week reading the actual USB specifications, engineering guides from chip makers like Renesas, and a stack of independent buying guides. This is the plain-English version — the stuff that decides whether your phone charges in 30 minutes or three hours.

Watts are the speed. mAh is the tank. Stop mixing them up.

Capacity and speed are two different numbers, and the box puts the impressive-looking one in the biggest font.

Capacity is measured in milliamp-hours (mAh). It tells you how much energy the battery inside holds — the size of the tank. Speed is measured in watts (W). It tells you how fast energy flows out of the port — the width of the pipe.

A 20,000mAh bank with a 5W output is worse for most people than a 10,000mAh bank with 30W output: the big one takes roughly three hours to take a phone from 20% to 80%, while the smaller one does it in about 35 minutes. I keep seeing this mistake in reviews — someone buys the biggest number on the shelf and then wonders why their phone crawls.

Here is the rough map of what wattage actually buys you:

Output	What it does
5–12W	Old-school slow charging. Fine for earbuds; painful for a modern phone.
18–30W USB-C PD	Fast-charges nearly any phone and most tablets. The practical minimum in 2026.
30–45W	Faster Samsung charging (with PPS) and full-speed iPad charging.
65–100W	Real laptop charging — ultrabooks and thin-and-lights refill at close to wall speed.
100–240W	Gaming laptops and workstations. Needs the right cable, not just the right brick.

One more thing people miss: your phone sets the ceiling. A 65W power bank connected to a phone that only accepts 18W will still charge at 18W. Buying more watts than your devices can use is just buying a heavier brick.

USB Power Delivery, in plain English

USB Power Delivery — USB PD — is the standard that lets a charger and a device negotiate a safe charging speed. Think of it as a short conversation every time you plug in: the device says what it can take, the charger says what it can give, and they agree on a voltage and current.

The version that matters in 2026 is PD 3.1. It split the power range into two tiers:

• SPR (Standard Power Range): up to 100W, at 5V, 9V, 15V or 20V. This covers phones, tablets and most ultrabooks. It has been the standard for years.
• EPR (Extended Power Range): up to 240W, adding 28V, 36V and 48V levels at up to 5A. This is the new tier for gaming laptops and workstations — a jump from 100W to 240W, the biggest power increase in USB history.

The catch: EPR only works when the charger, the cable and the device all agree. A 240W charger with a regular 100W cable tops out at 100W, and a laptop without EPR support won't ask for it. The negotiation is deliberately strict — pushing 48 volts through a cable that wasn't built for it would be a fire risk, so the standard refuses to guess.

If you only charge phones and tablets, PD 3.0's 100W ceiling was never your bottleneck. EPR matters if you own a laptop that charges above 100W — check its specs for EPR support before paying extra for a 140W or 240W brick.

PPS: the quiet feature that decides your real charging speed

Here is the feature almost nobody checks on the box, and it matters more than the headline wattage for a huge number of phones: PPS, or Programmable Power Supply.

Standard PD negotiates in fixed steps — 5V, 9V, 15V, 20V. PPS lets the charger adjust voltage in tiny 20-millivolt steps, matching the phone's battery almost exactly as it charges. That precision wastes less energy as heat — roughly 30–40% less during fast charging — so the phone holds its fastest speed longer instead of throttling back.

This is not a nice-to-have. Samsung's and Google Pixel's fastest charging modes require PPS. A 45W charger without PPS will charge a Samsung flagship noticeably slower than a 25W charger with PPS, because the phone simply won't accept the higher fixed voltage. If you own a Samsung or Pixel, "PD 3.1 + PPS" is the line to look for on the spec sheet, not the wattage in the headline.

The industry baseline for a good multi-port charger in 2026 is GaN + PD 3.1 + PPS, all three together. Any one of them alone is a half-finished product.

GaN: why today's chargers are half the size of the old ones

GaN stands for gallium nitride, a semiconductor material that replaces silicon in the charger's power transistors. It switches faster and wastes less energy as heat, which means the components around it can be smaller. The result: GaN chargers run about 40–50% smaller and roughly 30% cooler than silicon chargers at the same wattage, with efficiency around 93–95% at full load.

That is why a 65W charger today is the size of the old 18W Apple cube, and why 140W and 240W chargers can exist at all in a pocketable form — silicon simply can't do 240W in that footprint without cooking itself.

One thing worth clearing up: GaN and PD are not the same thing, and they are not interchangeable. GaN is hardware — the material the transistors are made of. PD is a protocol — the language the charger and device speak. A GaN charger without PD is just a small brick that charges slowly. A PD charger built on silicon works fine, it is just bigger and hotter. You want both, and in 2026 you can have both for not much money. The EU's common charger rules, which require USB-C on laptops sold in the EU from April 28, 2026, have pushed the whole market this way — PD 3.1 with EPR is now effectively the default spec for any serious charger.

Power banks: why 10,000mAh never gives you 10,000mAh

This is the part that feels like a trick until you understand the physics. A power bank's cells store energy at about 3.7 volts. Your phone charges at 5 volts or higher. Stepping the voltage up loses energy — conversion is never free — and the cable and the phone's own battery management take their cut too.

Across the guides I read, the real-world delivery rate lands consistently at about 60–70% of the printed number. I use 0.65 as my planning figure:

Usable mAh = printed mAh × 0.65 ÷ your phone's battery mAh = full charges

Worked example: a 20,000mAh bank holds about 13,000mAh of usable charge, and an iPhone 15 Pro has a 3,274mAh battery — 13,000 ÷ 3,274 is just under 4 full charges. A 10,000mAh bank gives you roughly 6,500mAh usable, about 1.5 to 2 charges for most phones.

Printed capacity	Usable (approx.)	Phone charges	Best for
5,000mAh	~3,250mAh	Less than 1	Emergency top-up
10,000mAh	~6,500mAh	1.5–2	Daily carry
20,000mAh	~13,000mAh	3–4	Weekend trips
26,800mAh	~17,400mAh	4–5	Laptop + travel

One fraud check: a bank claiming 30,000mAh that weighs about the same as a 10,000mAh one is almost certainly fake. Real capacity has real weight — a 20,000mAh bank weighs roughly 400 grams.

And the phones themselves keep getting bigger batteries — Motorola's new Signature 27 ships with a 7,000mAh cell, and our launch coverage has the details. Some 2026 flagships have gone further still, with 10,000mAh phones now on the market — a trend that shrinks how often you need a power bank at all.

The airline rule: 100 watt-hours, and how to check yours

Airlines regulate power banks by watt-hours (Wh), not milliamp-hours, under rules shared by the FAA, TSA and IATA. The thresholds are simple:

• Under 100Wh: allowed in carry-on with no airline approval needed. This covers essentially every phone-focused bank up to about 27,000mAh.
• 100–160Wh: allowed only with the airline's approval.
• Above 160Wh: not allowed on passenger flights at all.

To convert: Wh = mAh × 3.7 ÷ 1,000. A 20,000mAh bank is about 74Wh; a 26,800mAh bank lands around 99Wh — just under the line, which is why so many laptop banks are sold at exactly 26,800mAh. Reputable brands print the Wh figure on the housing, and that number is what security reads.

And the rule people forget: power banks go in hand luggage, never in checked baggage. Every time.

The cable is half the charger

I left the cable for last because it is the piece everyone already owns and nobody thinks about — and it can quietly cap everything else.

USB-C cables carry an e-marker chip that tells the charger what the cable can handle. A cable rated for 60W will not pass 100W, no matter what brick you plug it into. Above 60W you need a 5-amp e-marked cable, and 240W EPR charging needs an EPR-rated e-marker built for 48 volts — with the wrong cable, the negotiation simply won't complete.

If you buy one upgrade this year, make it a good 100W USB-C cable with a visible wattage rating — a few dollars that removes the most common invisible bottleneck in the chain. Wondering why a fancy new charger runs slowly? Check the cable before you blame the charger.

How to pick: a 60-second decision framework

Forget the spec-sheet arms race. Answer three questions and the right product picks itself:

1. What are you charging? Phones and tablets only: 20–30W with PPS is plenty. Add a laptop: 65W minimum, 100W+ if it's a bigger machine — and if you're buying the laptop too, our laptop buying guide explains the processor, RAM and storage side of that decision. A gaming laptop: look for PD 3.1 EPR at 140W or 240W.

2. Where are you charging? At a desk, one multi-port GaN charger replaces three bricks. On the move, a 10,000mAh bank covers a day; a 20,000mAh bank covers a weekend. Flying: stay under 100Wh, which means 27,000mAh or less.

3. How many devices at once? Multi-port chargers split their wattage. A "65W" two-port charger might give 45W + 20W, or 65W to one port only when the other is empty — the headline number is the total, not per port.

My own setup after all this: one 65W GaN charger with PD 3.1 and PPS on my desk, a 20,000mAh bank with 30W output and a built-in USB-C cable for travel, and a single 100W e-marked cable in my bag. Phone, tablet, laptop — covered.

Three myths worth dropping

"More watts always means faster charging." No — your device sets the ceiling and the cable sets the floor. A 240W brick charges a phone exactly as fast as a good 30W PPS charger.

"A 20,000mAh bank gives you 20,000mAh." It gives you about 13,000mAh at your phone's port. Plan with the 0.65 rule and you'll never be disappointed.

"GaN means fast charging." GaN means small and cool. PD and PPS mean fast. You need the letters together — GaN + PD 3.1 + PPS — before the speed shows up.

Frequently Asked Questions

What wattage charger do I need for my phone?
For most phones, 20–30W with USB PD and PPS is the sweet spot. iPhones fast-charge at around 20–27W, and Samsung's fastest mode needs PPS more than raw watts. Anything above 30W only helps if you also charge a tablet or laptop from the same brick.

Is a 65W charger safe for a phone that only takes 25W?
Yes. USB PD is a negotiation, not a firehose — the charger and phone agree on a safe speed, and the phone will only draw what it can handle. The extra wattage just sits unused until you plug in a device that can take it.

Can I take a 20,000mAh power bank on a plane?
Yes, in your carry-on bag. A 20,000mAh bank is about 74Wh, well under the 100Wh limit that needs no airline approval. Keep it in hand luggage — power banks are never allowed in checked baggage.

Do I need a special cable for 100W or 240W charging?
Yes. Above 60W you need a 5-amp cable with an e-marker chip, and 240W EPR charging needs an EPR-rated cable built for 48V. With the wrong cable, the charger and device simply negotiate down to a lower speed — or refuse the high-power mode entirely.

About the Author

Sidra Salman is the founder of Electronic Media, where she writes practical, research-backed guides on consumer electronics, gadgets and home entertainment tech. Every guide is tested and written in plain English for a US audience.