Before you connect, make sure you know which pin is +, gnd on power supply and battery.
Use a home made or DIY connector to connect your power supply and battery, in between a current limit resistor is required.
For a 12.6V(3*4.2) battery, I use a transformer AC/DC 12V adaptor <2A directly connect the + to battery charge +, - to ground. That adapter open voltage is 12*1.414V loaded voltage is 12V so that no resistor in middle is safe and higher than 12.6 V can charge. But not leave the connection too long time, for test pupose 1 hour (1~2AH) charge should be good enough.
For a 16.8V(4*4.2) battery, a similar 16V adapter could be used.
If you use 19V adapter, series a risistor 5~10ohm 10W in the charge wire.