Yes, simply connect the external power supply's positive and negative outputs to the + and - connectors on the MagWLED-1 terminal block. Ensure that the voltage applied matches the LED strip's target voltage. MagWLED-1 will automatically step that voltage down to power the microcontroller.
Your LED strip might have convenient power injection wires available at the input, in which case you can keep the included pigtail connector inserted and inject power as per this photo:
If not, you will likely want to remove the included pigtail connector. Split the power supply's input and outputs with a "Y split" and then replace the pigtail's red wire (see photo below) with one of the positive outputs from the power supply and the pigtail's black wire with the power supply ground cable.
Important considerations when using external power!
Please add an inline fuse between the power supply and MagWLED / the LED strip. MagWLED-1 has a built-in fuse, but this fuse is "circumvented" when powering externally.
Do NOT power the board by DC and USB power at the same time. This can cause current to flow between the two power sources!
Voltage above 12V will likely destroy the MagWLED controller. If you want to drive higher voltages, you need to power MagWLED separately, either though USB-C, as step-down converter or additional power supply. Make sure to connect MagWLED's ground with the external ground, but leave MagWLED's positive output disconnected.