I am powering my 6500 with an Astron 70-m using the factory supplied power cable. When monitoring the voltage with K9DUR's SDRMonitor I see a RX voltage of 12.59 and a TX voltage of 13.45. Is that spread acceptable?
The radio needs to have 13.8 VDC at the radio on transmit (under load at full power). I would expect some IR (voltage) drop due to contact resistance, length of the power cable and if you are using a fuse/distribution block. You may have to increase the supply output voltage to compensate for the IR drop.