Using Firestick 4K on Windows via a Video Capture Card

I have just bought a video capture card. It has a HDMI input and a USB 3.0 output.

I have connected the Firestick to the video capture card, via the HDMI input and connected the output to a USB 3.0 socket on my computer. This is a fairly modern i5 Windows 11 computer so it should be able to handle the task OK.

As the original Firestick power supply is rather integrated into the TV wiring I have powered the Firestick using a RAVPower 40W 4-port power supply rated at 5V/2.4A per port. I am not using this source to power any other devices.

I then ran OBS Studio and made the recommended settings and the usual Firestick Window, rather slowly, on the computer screen. Once I had connected the Firestick to my 5G wifi

However every minute or so the screen goes blank and this is then replaced by a colourful multi striped screen. After a while the Firestick starts up again.

I have tried a couple of other power sources all rated around 5V/2A but with similar results.

Any ideas as to what has gone wrong?

If the video card is suspected can you recommend a suitable replacement - one of the cheaper ones if possible?