The Same Power Bank, Two Ports: 62.3 W and 5.3 W

The USB-A port on Anker's 20,000mAh power bank, measured on a MacBook Air M5: 5.3 W at 4 V. The same bank's USB-C port delivers 62.3 W.

The USB-A port on Anker’s 20,000 mAh power bank, tested against a MacBook Air M5 with a low battery, per the methodology.

This is the cleanest experiment in the series, because nothing varies but the socket. The same bank’s USB-C port was measured at 62.3 W. Same cells, same charge, same Mac, minutes apart.

The numbers

Rated12 W
Negotiated~8 W (5 V up to 1.5 A)
Live draw5.3 W (4 V at 1.31 A)
ProtocolUSB BC 1.2

Profile menu: one entry - ~8 W (5 V up to 1.5 A). There is no ladder.

Twelve times, from one decision

Port on the same bankDelivered
USB-C62.3 W
USB-A5.3 W

The bank is not rationing power to the USB-A port. It physically cannot do better there, because USB-A has no mechanism for asking.

USB Power Delivery negotiates over the CC pins, and those exist only on USB-C. A USB-A port has no CC pins, so there is no conversation to have — both ends fall back to the oldest thing they share, USB Battery Charging 1.2, which permits 1.5 A at 5 V. That is 7.5 W, full stop, and no amount of capacity behind the socket changes it.

So a 20,000 mAh bank with 87 W of USB-C output sitting right beside it delivers less through its USB-A socket than a desk power strip does.

It does not even reach the 7.5 W ceiling

The contract says 5 V at up to 1.5 A. The measurement says 4 V at 1.31 A.

USB specifies a downstream port between 4.75 V and 5.25 V. Under load this rail sits a full three-quarters of a volt below the floor, and the current follows it down. The standard is not what is holding this back — the standard is offering 7.5 W and the hardware is delivering 5.3 W of it.

This is a current, well-regarded 2023 power bank. That is what makes it worth writing down. A sagging rail is easy to explain away on a 2014 bank or a 2004 router — ageing cells, tired converters, hardware past its service life. This one is none of those things.

What it is, instead, is a USB-C-first product where the USB-A socket is a legacy courtesy. All the design effort went into the port that reaches 62.3 W. The old one is there because people still carry old cables, and it is built to the standard of a phone charger from a decade ago, because that is all it is expected to be.

What to do about it

Use the USB-C port. That is the whole lesson, and it is worth saying plainly because the USB-A socket is right there and looks equally capable.

If you are carrying this bank specifically to keep a laptop alive, the cable matters too: at 62.3 W the USB-C side draws more than 3 A, which requires a 5 A e-marked cable. Plug the same bank into a plain 3 A cable and you land at 60 W — still twelve times the USB-A port, but not what the bank can do.

The unit

The Anker 20,000mAh power bank with a built-in USB-C cable, 87 W maximum.

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