Yep. Although some less reputable mini-system manufacturers tend to quote "music power" or in your case dynamic power, the RMS value is always the standard value for power measurement. So yours has 40W.
Some boombox companies even quote PMPO (or Peak Music Power Output) which is normally 4-8 times RMS, and with both channels added...so a £15 boom box from your local supermarket ends up having 60W, instead of the 3-4w RMS per channel that it's actually got!!!