Problem running Jebao powerhead off Apex - not sure what's broken

[makana]

Glad to hear you got it figured out.

A resistor in series will reduce current. It seems to me that they use it in such a way that it divides the voltage in the adaptor. At least from what I remember when I was reading up on the DIY version.

What you will see with a bad power supply is full voltage when there is no load. When you try to power something with it, the voltage drops because it is no longer producing enough current to maintain the voltage. The trouble is, it can be difficult to test the voltage when everything is connected.

For testing amperage you need to have the meter connected in series, which again can be difficult. You take the positive power source and run it to the meter and then run the other lead of the meter to the device. On most meters you also have to move the red lead to the amp connection.