macbook dual monitors

Hi

I have been using my 2016 12" Macbook with an external monitor for ages and have acquired a second monitor. Both displays use HDMI to VGA cables with an external power source plugged into a separate usb plug for power to the monitors.

I have bought a HDMI splitter to plug into the macbook and then plug both of the monitors into that. Both monitors work perfectly on their own but when i use the splitter, neither of them work. Am i doing something wrong (ie. does USB-C not support 2 HDMI outputs) or should it work and maybe the splitter is just broken. I dont want to buy another one if it will not work at all.

Many thanks

for clarification, the setup is:

Macbook USB-C to HDMI to HDMI SPLITTER with each monitor plugged into that.