I had to replace the fan belt on my race built 2065 motor. The replacement belt is made in China and at high rpms it kept flying off! Has anyone had this problem and is there a solution?

It is less likely a counry of origin issue and more likely a hardware problem.
There is a recent thread here concerning belt / alignment / brackets

I only use Contitech belts because they are very durable and fit well same as I only use OEM oil filters but that's just me.
Make sure your altenator pulley isn't worn and polished up (slippage) ,make sure you check the mounting brackets (as mentioned) ,try to do a basic alignment before tensioning the belt.

Gates makes a belt with ribs on the exterior
It’s is superior to most other belts

There is a trick for high rpm belt slip and racing... but not good for the street and charging. So a better belt is the 1st step

Then check the pulleys or replace would be next

the new continental/ ContiTech are made in .......white letters since 2014

Make sure you are using the correct size belt. 9.5 x 965 mm or 021.903.137A

This was a fairly common issue for track use or auto-x drivers since quick RPM changes were common. Even with all the brackets and pulleys in good shape and properly aligned the high RPM could throw the belt just from normal stretch.

On track cars or Auto-x only cars we used to run a narrower belt that fit deeper in the pulley and was less likely to come off at high RPM.
It was a domestic sized belt that I think was 7/16 wide or about 8mm but I am not sure.

These did not have lifespan a belt should have for a street car but they stayed on track/auto-x cars.

I still have an old one but I don't think it has numbers on it anymore.

Jim

9.5 mm are you sure ? I thought it was 10 x 965 ?,2 of my engines have that size belt...not saying you are wrong but TBH have never checked.

Belt

I had a repetitive belt slipping issue. Turned out the alternator pulley was cracked.

The mount bracket for the alt. My car made a chirping sound when running and I could never get the belt to remain tight.

I will try a thiner belt (8mm) since the alignment was fine before I started having this problem. Thanks for all of the input.

After Marks comment about belt size I checked my supply and also found an 8 X 965mm,tryed it on my spare T4 motor (next build) and as Jim mentioned it fitted better in the grooves ,and was level with the top of both pulleys,even being a bit worn the adjustment was about centre on my altenator top bracket
Considering any part of the belt not fully contacting the pulley vee's is lost drive ,perhaps the narrower belt is the way to go.