Where do you find "AC caps"?
All non-electrolytic caps (and non-polar electros) will handle AC.
The difference is: a little AC or big AC?
A motor-start capacitor has to pass hundreds of watts of power while shifting its phase to twist an AC motor into starting. A large array of poly-film caps can do this, at high cost. The motor-start cap is designed for the starting voltage, starting current, and start-up duration, to be just good enough at lowest cost.
Across-the-line caps suppress radio interference. If they short-out, the cord could burn, or the chassis might be connected to the live wire. Electric Safety Agencies issue specific rules and tests for such applications. These caps should cost more than a non-safety-rated cap. However because they are used in EVERYthing, sometimes you can get them cheaper.
AC caps will be rated in AC Volts. There is not any strict translation to DC Volts, or vise versa. A 600V DC Orange Drop can handle 550V DC plus 20V audio AC forever, but 400V pure AC may kill it. A 240V motor-start cap can probably take way more than 240V DC, but how much more? And for how long? (Motor-start duty is just a few seconds, rarely more than a few times per hour, and often not warranted more than a few years.)
Frequency matters. Series resistance which causes slight heating at 60Hz would cause extreme heating for large 10KHz AC curent. Historically, this meant that motor-start caps were all film caps (or nasty wet electrolytic); however recent improvements in dry nonpolar electros make this practical (good-enough and cheaper) in motor-start duty.
In general, caps rated for heavy AC will be more expensive.
In most audio applications, "all" caps will be DC rated. Our DC voltages are much larger than our audio voltages. This includes the large bulk capacitor in the power supply (anyway, a polar electro is perfect here and much cheaper than any alternative).
The main exception would be capacitors across your 120V/230V wall-power line and switch, used to supress radio interference and contact clicks. We used to use plain 400V wax-caps on 120v lines, but these fail in a few years or decades, which is why line-rated caps exist.