You need to check multiple variables, Is often healthy to measure it with a Oscilloscope and with a current meter.
Tipically 3 factors that can affect the powering up of the Teltonika devices
1. Polarity: make sure that you are using Cotinuous Current and the correct polarity
2. Current supplied: Make sure that the power Supply is delivering at least 1A when the router is connected.
3. Noise in powerlines. If the power supply is not stable nough the device CPU won't be able to start propperly and will hang up until cleant current is provided to the unit.