Hi Trottsky,
I'm glad to see the USB-C power suggestion shadowsports made is working for you. In regards to the dummy battery issue we would recommend loading a Canon battery in the camera and check to see if the same thing happens. When you check this done have any other power sources connected. If this same thing happens with a battery loaded by itself that indicates there is an issue with the camera. If it is only happening when you have the dummy battery loaded that indicates there is an issue with the dummy battery.
If the issue is with the dummy battery we would recommend contacting the maker of the dummy battery. Through Canon support we only have information on products made by Canon itself. If you want to try the Canon dummy battery power adapter there are two pieces to it and you would need both. The DC Coupler DR-E6C is the part that plugs into the battery compartment and the AC Adapter CA-946 is the part that plugs into your power supply.
If the issue is happening with a Canon battery loaded in the camera we would recommend sending the camera in for repair.
The Canon U.S.A., Inc. online repair portal allows you to set up service in a few simple steps. The repair portal gives you the ability to set up service for multiple pieces of equipment at once, and to receive a repair estimate in the majority of cases, depending on your model and issue. The portal also allows you to upload images or videos that will assist us in repairing your product. You can also select how you wish to be notified of the progress of your repair. The portal's service history section allows you to view all services that have been performed on any of your camera or video products since January 7, 2020.
Please follow the link below to access our online repair portal to arrange for service:
https://mycanon.usa.canon.com/signin
Instructions for Accessing and Using the Online Repair Portal
You will need to access or create your My Canon Account.
If you already have a My Canon Account and your product is already registered, simply click on the “Get Repair Services” link on the left menu and follow the onscreen instructions to arrange for service for your product.
If you have a My Canon Account and your product is not registered, you must register your product first. Click on the “Get Repair Services” link on the left menu, then click on the “Register Product” link on the right. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product.
If you do not have a My Canon Account, you will need to create one. After you create your account, click on the “Add Product” link to register your first product. After your product is registered, click on the “Get Repair Service” link on the left menu and follow the onscreen instructions to arrange for service for your product.
Once you have completed the repair request, you will have an opportunity to print a copy of the request for your records. This request form will also contain shipping instructions and an address label that you will attach to the outside of your shipping box when mailing your equipment for repair.
Danny
