Corresponding to your case, I would set target of arc camera as target of universal:
universalCamera.setTarget(arcCamera.target)
In case of switching from arc to universal:
arcCamera.setTarget(universalCamera.getFrontPosition(arcCamera.radius))
The Playground:
Note: There might be special edge case on arcCamera.beta === 0, so that arc camera flips, because it only has an upVector and no forwardVector.