I emailed Sandisk to ask about this. They said “we don’t supply chargers for the Clip” (no kidding!) but recommended these:
PP: Thanks for forwarding the helpful charger links. The Amazon link is the first charger that I’ve seen that actually claims 4GB Clip compatiblity in the marketing stuff. Based on the numerous related posts on this forum, there is much confusion amongst the Clip user community regarding a compatible charger for 4GB clip, standard current output of USB ports, etc. Too bad somebody from Sansa is not willing to provide a definitive answer or specifictation, to clarify. From a consumer’s perspective, that does not seem to be asking much of them?
I also had a buzzing AC adapter. Worked fine but the sound bugged me–I returned it.
The company you bought from seems responsive. I’d call them for a replacement (I see in the Amazon.com comments that the seller did so for another buyer).