Could be anything, probably trash! Any approved caps or pills in the US MUST have identifiable markings of some kind to distinguish what it is. That is the law. I would throw it down the garbage disposal.
I am not a dr. My statements are based on years of experience and related education. Consult with the professional of your choice regarding matters of concern.
It's impossible to ID as it is. Clear capsules is one of the ways >>>>>> powder is traficked on the "to the user" level. Be particularly concerned if the capsule is only <50% full with powder - professionally produced vitamin supplements exist as you describe, but should be filled to the brim. Street >>>>>> usually isn't.
I agree with the orignal reply - garbage disposal.