TENINYU USB 2.0 A Male to DC 4.0x1.7mm 5 Volt DC Barrel Jack Power Cable 3FT (Max 2.5 Ampere Power Cable, Center PIN Positive), 2Pack https://www.amazon.com/dp/B01MR6DFAD/ref=cm_sw_r_cp_apa_i_4Q7QCbBK5MV81
This is the one i bought and The Mi Box turns on and gets to the Android screen and then it powers off and restarts in the Android screen but never goes beyond that.
You need to check the power output (both volts and amp) from your usb source to see if it is adequate for the Mi Box
i recall using my 1st gen chromecast in which my TV's USB would supply the power, but I doubt he can use the same port for a Mi Box. Please get a proper power adapter
Check the manual or search online, as stated above, I also doubt you would get enough power from the tv's usb port to power an android box, it may work with a "stick" device as those use less power, either way you really should be using the power adapter provided.
I doubt a USB port would have enough current to power a mi box. It came with a power supply, you need to be using that.