By type · Matching the label
DC power supplies: matching the label on your device.
Your device's input line reads something like "DC 12V 2A" or "5V⎓3A". Four things have to line up before a replacement works: voltage, current, polarity and plug size. Get one wrong and you either get nothing or you get smoke.
The four-part match
Voltage must be equal. This is the only one of the four with no tolerance worth gambling on. A 12V input wants 12V; 9V leaves it dead or unstable, and 19V can put the internal regulator past its rating. Manufacturers design for roughly ±5%, which is why a supply measuring 12.4V unloaded is still correct.
Current must be equal or greater. Amps are a ceiling, not a dose. A 12V 2A device is perfectly happy on a 12V 5A supply — it draws its 2A and leaves the rest. Going the other way is the failure case: an undersized supply sags under load, and a sagging rail is why routers reboot and external drives disconnect mid-copy.
Polarity must match. Barrel plugs are usually centre-positive, marked with a small diagram of a dot inside a C with a plus sign on the inner side. Centre-negative exists, mostly on audio equipment. Reversed polarity on an unprotected device is instantly fatal.
The plug must physically fit. Common barrel sizes are 5.5×2.1mm, 5.5×2.5mm, 4.0×1.7mm and 3.5×1.35mm, and 5.5×2.1 will slide loosely into a 5.5×2.5 socket while making poor contact.
Common output ratings and what they run
| Output rating | Watts (V × A) | Typically found on |
|---|---|---|
| 5V ⎓ 2A | 10W | Set-top boxes, single-board computers, USB hubs |
| 9V ⎓ 1A | 9W | Effects pedals, some modems |
| 12V ⎓ 1A | 12W | Broadband routers, LED strips, CCTV cameras |
| 12V ⎓ 2A | 24W | External hard drive enclosures, network switches, monitors |
| 12V ⎓ 5A | 60W | Larger monitors, mini PCs, powered speakers |
| 19V ⎓ 3.42A | 65W | Older barrel-plug laptops |
| 20V ⎓ 5A | 100W | USB-C laptops, delivered over the PD 20V rail |
Multiply volts by amps and you have watts, which is the number our wattage pages are organised around; the arithmetic and the reason amps behave as a ceiling are unpacked in amps, volts and watts.
Where USB-C fits, and where it does not
Power Delivery replaces the barrel plug with negotiated rails: 5V, 9V, 15V and 20V as fixed steps, plus 28V, 36V and 48V under PD 3.1. Two gaps catch people out. First, 12V is not a fixed PD rail — it was optional in early revisions and is not something a standard USB-C charger will hand a passive adapter cable, so a 12V router cannot simply be fed from a USB-C brick without a trigger cable that requests a PPS range covering 12V. Second, a barrel-to-USB-C pigtail with no electronics is a dead end: with no CC-line negotiation the charger stays at 5V.
Picks by output type
- 12V
12V Regulated Barrel Supply
The workhorse replacement for routers, switches and drive enclosures. Confirm the barrel size before ordering.
- Output
- 12V DC, regulated
- Plug
- 5.5×2.1mm typical
- Polarity
- Centre-positive
- 9V
9V Centre-Negative Pedal Supply
Audio pedals frequently invert polarity; a standard centre-positive brick will not do.
- Output
- 9V DC
- Plug
- 2.1mm
- Polarity
- Centre-negative
- PD
USB-C PD to DC Trigger Cable
Turns a modern PD brick into a fixed 9V, 12V or 20V barrel supply by requesting the rail over the CC lines.
- Input
- USB-C PD
- Output
- Selectable rail
- Note
- Electronics in the plug
For anything USB-C, skip the barrel section entirely and start at the adapter type index or the AC adapter page, which covers the conversion side of the same hardware. Multi-device setups are a different problem — see 2-port and 4-port adapters.
FAQ
Can I use a DC adapter with a higher amp rating?
Yes. The device draws the current it needs and no more, so a 12V 5A supply is a safe stand-in for a 12V 2A one. Only the voltage has to match exactly; extra amperage is headroom, not force.
What happens if the polarity is reversed?
On a device with reverse-polarity protection, nothing — it simply refuses to power on. On one without, the damage is immediate and usually terminal. Check the barrel diagram on both the device and the supply before plugging in.
Can a USB-C charger replace a 12V barrel supply?
Only with a trigger cable that negotiates the rail, because 12V is not a standard fixed Power Delivery voltage. A plain passive adapter cable leaves the charger sitting at 5V and the device dead.