Lets try a technical question. A few months ago Todd was gracious enough to give me a Yeasu FT-1500M VHF radio so that I did not have to pull my Kenwood TM-V71 radio I have mounted in my jeep out every time I wanted a base station to use at home. The radio seemed to be in good shape but I had issues getting it to transmit at higher power levels. It did fine at 5 and 10 watts and often but not always would be OK on 25 watts. Sometimes I would get a buzzing in my computer speakers but apparently no signal was going out (missed a net check in this way once). Trying to transmit at 50 watts would result in the radio restarting. Due to the age of the radio I attributed this to, well, the age of the radio, and since I could do what I needed with 10 or 25 watts I didn't think too hard on it.

Today I pulled my Kenwood out of my jeep and put it on my desk for some reprogramming and troubleshooting. Lo and behold it is having the SAME EXACT problem as the Yeasu.The Kenwood has no 25 watt setting, only 5, 10, and 50. It transmits fine on 5 and 10 but not on 50, though it does not shut off at 50 watts like the Yeasu does. This means that the issue I am having is not with the Yeasu but somewhere else in my setup. I ran this same Kenwood off this same power supply for a few weeks earlier in the year before I put it in my jeep and it worked fine. However the antenna I am using is different. I left my N9TAX roll up slim jim j-pole at field day and had to purchase another. I got another one from N9TAX and mounted it in a very similar position to the other.

Altogether this leaves me with basically two options as to what has gone wrong. Either there is some sort of issue with my antenna set up or my power supply is having issues. I am unfortunately leaning towards a power supply issue due to the readings I have been getting from its volt and amperage display while transmitting. With the Kenwood I am getting 12.8V, 0.5A receiving,  11.6V, 2.6A transmitting at 5 watts 11.4V, 3.7A at 10 watts, and 10.7V 7.1A at 50 watts. With the Yeasu I am getting 13.3V, 0.2A receiving,  11.6V, 2.3A transmitting at 5 watts, 11.4V, 3.0A at 10 watts, 11V, 5A at 25 watts, and it restarts at 50 watts. One oddity I have noticed that that with the Yeasu on 25 watts I can hit certain repeaters but not other. If I drop the power to 10 watts I can hit everything again. All in all this is quite strange and I don;t know how to fix it. 

My first suspicion would be power supply since both radios are exhibiting similar behavior.  What is the make, model & rating of the power supply you are using?

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I agree, I have also seen “strange behavior” using different power supplies on my FT-857. Experiment with power supplies first in my opinion. Of course my opinion isn’t worth much.