600 watt power supply settles in at 50w charging YetiX 1500

I bought the YetiX 1500 and the 600w charger at the same time. Have tried many times to charge the 1500 with it, and when it first starts charging, it shows the rate at nearly 600w. But it only holds that rate for about one minute. Then for no apparent reason, the charging rate sits back down to about 50w.

I can turn off or unplug the charger, restart the charging, and it gets back up to 600w, but only for that same minute again, then it’s back to 50w.

ive confirmed the firmware of the 1500 is current. Any other ideas? Otherwise I’m gonna return the charger to REI.