USB chargers that give more than 5V?

[Tom41]

I recently bought a portable label printer with a USB port that allows you to charge the internal battery. It comes with a USB-A to Micro-USB cable, but no charging plug. A sticker next to the charging port says "Warning! Do not use adapter with voltage over 5V!"

Thing is, are there any USB chargers that give out more than 5V, and in what situation would that be used? Just to be on the safe side I used a multimeter to measure my chargers - one is giving out 5.11V, the other is giving out 4.9V. The warning sticker suggests the printer doesn't have any overvoltage protection circuit, which could be a nasty surprise for someone...

[m1ch43lzm]

Some mobile phone chargers with USB-A port do have multiple output voltages, example: Qualcomm Quick Charge 2.0/3.0 or other competing standards before USB PD was standardized among phone manufacturers
Check the label of your charger if it lists multiple output voltages
At least on QC2.0/3.0 chargers they start at 5V, when a compatible phone is connected it negotiates higher voltage, can't speak for other "fast charge" standards

[stj]

all usb chargers are 5v -even QC types are 5v unless they recieve commands to up the output.
the real thing to watch is the current.
how much does the printer need?
most cheap chargers are 1A, old ones from companies like samsung, nokia etc arent even that much sometimes.

[mon2]

Some are a bit higher than 5v to compensate for the voltage drop from the copper wiring and/or forward voltage drop of diodes on the target board. For example, the raspberry Pi power adapter. Will not kill the widget as the voltage is within tolerance specifications.