Chargers and Power Delivery, Explained: PD, GaN, and Wattage

Specs are marketing, and "fast charging" is one of the vaguest specs in the aisle. A charger does not have a speed; it has a wattage it can offer and a negotiation it runs with your device, and if you get either wrong you end up with a handheld that charges slowly, or drains while it is plugged in. This is the explainer that turns "fast charging" into numbers you can predict. If you want the battery-runtime side of the math — turning watts into playtime — that lives in our TDP and battery-life math guide; this one is about putting energy back in.

USB Power Delivery: a negotiation, not a speed

Modern handhelds charge over USB Power Delivery (USB PD), a standard where the charger advertises a menu of power profiles and the device picks the highest one it supports. The menu entries are Power Data Objects (PDOs) — fixed voltage steps at 5V, 9V, 12V, 15V, and 20V, each with a maximum current. Wattage is just volts times amps, so a charger offering 20V at 5A can deliver 100W; one that tops out at 5V/3A can only deliver 15W no matter what it claims on the box. The device and charger meet at the best profile both support.

Two refinements matter. PPS (Programmable Power Supply) lets a charger fine-tune voltage in small steps rather than jumping between fixed rungs, which runs cooler and slightly more efficiently — worth having, not worth obsessing over. And PD 3.1 EPR extends the standard past 100W toward 240W using higher voltages; it is real, but no handheld needs it, so do not pay for EPR to charge a device that draws 65W. The practical takeaway: a charger is only as useful as the highest PDO your handheld will accept, so match the profile, not the marketing adjective.

Wattage: the charger must beat your draw

Here is the arithmetic that decides whether "plugged in" actually means charging. Manufacturers ship a charger sized to the device — a Steam Deck ships a 45W charger, a ROG Ally and Ally X ship 65W — and those are the floors that charge at full rate. The complication is playing while charging. If your handheld pulls 25W running a game and the charger supplies 45W, the surplus (about 20W) trickles into the battery while you play — slow, but a net gain. But if you are running a demanding title that pulls 30W and charging from an underpowered 18W source, the device draws the difference from its own battery, so it drains while plugged in. The rule is blunt: to charge and play at once, the charger must supply more watts than the game draws. Undersize it and the wall outlet just slows the drain instead of reversing it.

GaN: the same watts in a smaller, cooler brick

GaN — gallium nitride — is a semiconductor that switches faster and wastes less energy as heat than the silicon in older chargers. The practical result is that a modern 65W GaN charger is dramatically smaller, lighter, and cooler-running than the bulky 65W brick of a few years ago, and many GaN units pack multiple ports into a travel-friendly size. GaN does not charge faster at a given wattage — 65W is 65W — but it delivers those watts in a package you will actually pack, which is why it dominates our best chargers and power banks picks and our handheld travel kit recommendations. Buy the wattage your device wants; buy it in GaN so it does not weigh down the bag.

Charge-time math, worked honestly

You can estimate a charge time the same way you estimate runtime: energy divided by power, with an honest correction. A 50 Wh Steam Deck OLED on its 45W charger looks like 50 / 45 ≈ 1.1 hours of pure energy transfer — but real charging is not constant. Lithium cells charge fast up to roughly 80%, then the charger tapers current in a constant-voltage phase to protect the cell, so the last 20% is slow. Add the taper and normal conversion losses and expect closer to 1.5 to 2 hours to a true 100%. An 80 Wh ROG Ally X on 65W works out the same way: about 1.2 hours of raw transfer, roughly 2 hours to full with the taper. The useful habit that falls out of this: charging to 80% is much faster per percent than the final stretch, which happens to align with the battery-longevity advice in our battery care guide — stopping at 80% is both quicker and kinder to the cell.

Power banks: the watt-hour and airline math

A power bank is rated in mAh at the cell's ~3.7V, which overstates the energy you actually get out. Convert to watt-hours to compare honestly: a 20,000 mAh bank is about 74 Wh (20,000 x 3.7 / 1000), and because the bank boosts to PD voltages at roughly 85-90% efficiency, you get closer to 60-65 Wh delivered. That is enough to refill a 50 Wh Deck a bit more than once, or a ~19 Wh Android retro handheld three times. Two rules make a power bank useful rather than decorative:

1. Output wattage must cover your draw, exactly like a wall charger. A bank that only pushes 18W will not keep a Windows handheld alive under load, no matter how large its capacity — check the PD output rating, not just the mAh.
2. Airlines cap lithium capacity by watt-hours. Batteries up to 100 Wh ride in carry-on freely; 100-160 Wh needs airline approval and is limited to two spares; above 160 Wh is prohibited. Spare batteries and power banks must go in the cabin, never checked. Most 20,000 mAh banks sit safely under the 100 Wh line, which is why they are the travel default.

The cable is the quiet failure point

The most overlooked part of the chain is the cable. A USB-C cable rated for only 3A (60W) will throttle a 100W charger to 60W, because carrying more than 3A safely requires a 5A-rated cable with an e-marker chip inside it. Pair a great charger and a great dock with a cheap thin cable and you have quietly capped your whole setup — and this is a common cause of "why is it charging so slowly" that no amount of charger wattage fixes. For any 100W path (including a dock's passthrough, covered in our docks and hubs deep dive), use a 5A/100W-rated cable and stop guessing.

The verdict

Charging a handheld is four numbers, not a marketing word. Confirm the charger offers a PDO wattage your device accepts; make sure that wattage beats your gaming draw if you want to play and charge; buy it in GaN so it fits the bag; and feed it through a 5A-rated cable so nothing throttles. Size a power bank in watt-hours, check its output wattage, and keep it under 100 Wh for flights. Specs are marketing; the verdict on chargers is that "fast" is meaningless and watts are everything — get the wattage and the cable right, and every device in your bag charges as fast as its own silicon allows.