NorioDS Yeah man, that should work just fine ?

Regarding the polarity, you generally shouldn't have an issue - only some pedal manufacturers do things differently (can't think of any offhand) but most would be compatible with the Boss power supply (especially boss pedals with the boss power supply).

The reason that is so pricey is that it's a regulated power supply this (after polarity and mA supply) is most important. The reason that unregulated power supplies are so cheap is (and I might be slightly off with this but the sentiment is precise) because they are designed to produce a certain voltage at a particular current. So, if say you have a 500mA unregulated power supply and your device draws 200mA, that device would not be receiving 9V of power (voltage decreases as current increases and the same is true in reverse).

Regulated power supplies like that Boss one have a voltage regulator to ensure that regardless of current pull (mA), the voltage will remain constant at 9V. Without the voltage being regulated, you could be introducing a crap ton of noise as your pedal could potentially be receiving a higher voltage than it's built to (or alternatively, it could function sub-optimally if receiving less voltage than its expecting). Quality devices are built to tolerances so it might be safe to receive extra or less voltage (to a point of course - 12V would probably kill a 9V device) but I just think its safer (and more optimal) to just go with a regulated power supply in spite of the cost.

One upside though is that you can use it to power the recorder or for pedals (just not more than 500mA obviously and double check that the polarity images match) so it's a worthwhile purchase for sure. For reference, with discount, I paid R500 for that same power supply at TOMS a month or two ago.