Yes, that is a very basic rectifier. The device sounds like it has a rectifier already in it, it accepts up to 150VAC, right?
That would not solve the transient spikes from the alternator, though. Where you're gonna solve the problem is filtering. But you would not really want to try to filter AC, you want to filter out AC in this case and it's more complex than needs to be. Large value caps tend to be polarized and so you would have to be careful not to reverse the polarity, thus the blocking diode(s).
Something that occurred to me, you might try this filter. It's very basic but does work to cure alternator whine when operating HF mobile (which remember is running from already rectified power). They used a 4700uF cap to swamp the power, but it won't hurt anything to put a couple small values in, too. I'd put in a 1uF and 0.01uF as well. This is essentially just a monster low pass filter and the smaller values are for high frequency noise.