The Raspberry Pi 5 needs a 27W USB-C PD supply because it requests 5V at 5A to power the BCM2712 board and high-draw USB peripherals at full speed. A lower-rated charger triggers a low-voltage warning and limits USB port power delivery.
Plenty of perfectly good USB-C chargers fail the moment you plug them into a Raspberry Pi 5, and the reason is a single, unusual power request. The Raspberry Pi 5 asks for 5V at 5A, which is 27W, and most chargers simply cannot offer that exact combination over USB-C Power Delivery, so the board throttles its USB ports or warns about low voltage.
The Pi 5 negotiates a 5V/5A (27W) profile over USB-C PD to run the faster BCM2712 processor and still leave enough current for power-hungry USB peripherals. Chargers that top out at 5V/3A make the board limit total USB output to protect itself, and weak supplies trigger an under-voltage warning. Use the official 27W supply, or a PD charger that genuinely advertises 5V/5A.
Standard USB-C PD chargers reach high wattage by raising voltage, not current. A typical 27W phone charger delivers it as roughly 9V at 3A, or 15V at lower current, then a chip inside the device steps it back down. The Pi 5 runs its main rails directly from 5V, so it needs the wattage delivered as raw current at 5V rather than at a higher voltage. Few third-party chargers offer a 5V/5A profile at all, which is why a charger that powers a laptop happily can still leave the Pi short.
When the Pi 5 cannot negotiate the 5A profile, it assumes only 3A is available. To stay within that budget it caps the total current going to the USB ports, so an external SSD or a hungry USB device may not spin up or may disconnect under load. You will also see the low-voltage warning, a lightning-bolt icon or a logged "under-voltage detected" message, whenever the supply sags below the safe threshold.
This is not only about the charger. A thin or non-compliant USB-C cable causes voltage drop along its length, and the official supply deliberately uses thick conductors to avoid that. USB-C extension cables are a frequent culprit because they often break PD compliance and create false warnings even with a good charger.
The simplest fix is the official 27W USB-C supply, which is built to deliver the 5V/5A profile the Pi expects with a cable thick enough to avoid drop. If you prefer a third party unit, check the specification sheet, not just the wattage number, and confirm it explicitly lists a 5V/5A PD profile rather than only higher-voltage profiles.
If you only run the board with light peripherals you can often get by on 5V/3A, but the moment you add SSDs, cameras or a hub, the headroom of the 27W supply matters. Compact builds like the Pi 5 sit alongside the rest of our mini PC and small-form-factor range at Evetech for anyone weighing a single-board computer against a low-power mini PC.
Only with limits. A 5V/3A phone charger will boot the board, but the Pi caps USB port power and may warn about under-voltage when peripherals draw current. For full performance you need a supply that offers 5V/5A.
Because it has no way to know more current is safe. Without a negotiated 5A PD profile, the Pi budgets for 3A total and reserves enough for the board, leaving less for the USB ports to avoid browning out.
Not always. A compliant charger paired with a thin or extended USB-C cable can still cause voltage drop and trigger the warning. Use a short, good-quality cable, and avoid USB-C extensions.
The board itself uses far less than 27W under normal load. The 27W rating exists to provide headroom for peak processor demand plus the current that connected USB peripherals can draw at the same time.
Building a compact home server or single-board project? Compare small-form-factor options in the mini PC range at Evetech to find the right low-power machine for the job: https://www.evetech.co.za/PC-Components/mini-pcs-194
Only with limits. A 5V/3A phone charger will boot the board, but the Pi caps USB port power and may warn about under-voltage when peripherals draw current. For full performance you need a supply that offers 5V/5A.
Because it has no way to know more current is safe. Without a negotiated 5A PD profile, the Pi budgets for 3A total and reserves enough for the board, leaving less for the USB ports to avoid browning out.
Not always. A compliant charger paired with a thin or extended USB-C cable can still cause voltage drop and trigger the warning. Use a short, good-quality cable, and avoid USB-C extensions.
The board itself uses far less than 27W under normal load. The 27W rating exists to provide headroom for peak processor demand plus the current that connected USB peripherals can draw at the same time.
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