The MPS-850 needs 9V/2A and it is not easy to get a good power supply for this particular voltage/current combination. The previous one we had gave up because it caused a feedback hum through the USB interface once the MPS-850 was powered off, so it was constantly being unplugged, and one of the pins came loose.
I would like to pay more for a higher quality component of the sound production chain. Ideally one that turns itself off when not in use. Or, the MPS-850 should be switched to USB power for both the main unit and the hi-hat, so that we can use one of the many power supplies we already have.
Otherwise, Thomann are an excellent source of musical bits and bobs.