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I have no charger atm and I am a bit strict on money right now.
Anyways, I have a spare Samsung charger and it has 2 values.
It's a fast charger so I don't know what applies to the Pi.
Also = the "=" sign has a full line on top and 3 small lines under it.
This charger has the so called "Adaptive Fast Charging" (see here) with an output voltage of 9V or 5V. While the 9V are way out of the Pi's spec, 5V are perfectly fine (see Raspberry Pi Power Limitations for all the details).
So the real question here is, how and when does the charger output 9V? Obviously anything that comes with a micro-USB should not be outputting a voltage outside of USB spec (the 5V) per default. Thus all higher voltages should only be applied after the device and the charger negotiated that.
According to this post:
Samsung's adaptive fast charging uses Qualcomm’s Quick Charge 2.0 (QC2.0) protocol. This protocol allows the phone to switch the charging output voltage of the adapter to 5V, 9V, 12V, or 20V up to 3A using the USB D+/D- pins.
Increasing the output voltage of the charger requires the connected device to apply certain voltage levels to the USB data lines. Those data lines are not connected on the Pi 3's powering micro-USB connector (see schematics). So the Pi cannot (accidentially) increase the voltage.
More about fast charging standards: How does fast charging work? Here’s every fast charging standard compared. Which unfortunately states that Samsung's Adaptive Fast Charging differs from Qualcomm's Quick charge.
In conclusion I would strongly guess, while not 100% sure, that it is ok to use this charger with the Pi.
