R96, the phrasing of your question seems to suggest that this is something we should be buying routinely. On the contrary, as Alan points out, the power supply sections of competently designed AV equipment condition the AC from the wall socket into clean DC for the amplification section to use. No additional "conditioning" is needed, despite the BS-laden claims of some sellers to the contrary.
As to protection from surges, again the power supply sections handle moderately high surges routinely. There may be some occasion on which a surge protector(say about $20)might be of benefit on surges which couldn't be handled routinely but yet weren't so powerful(e.g., a near-direct lightning strike)as to make any protection useless. I use nothing of this sort either and as I've told my good friend Jack(Ajax)to his delight, if a lightning strike destroyed my equipment I'd view it as simply being God's way of telling me that it's time to upgrade.
