External power on a 8 channel relayboard WITHOUT JD-VCC

I have two 8-channel relay modules from funduino. Because my Arduino Mega won't be able to power them all I'm using a external 5v 1.5A power supply. All the information I find points towards a JD-VCC header for the external power supply, but my boards don't have these:

How do I connect the external power supply to the modules? And do I connect the GND of the Arduino to the GND of the supply?

Thanks in advance!

Just connect the VCC of the relay module to external power supply and connect the gnd of both the mega and module together

Don't connect the grounds together if you want/need opto isolation.

Post a link to the module you have.

What does that com/gnd jumper in your (invisible) pasteboard pic do?