When splitting signals via any Active RF splitter the power provided by the RF Out on a DSTV decoder or any other RF out on a device is enough to power the Active RF Splitter when 2 or more splitters are cascaded. When cascading more than one Active RF e.g 1x4 Active RF cascaded onto a 1x2 or another 1x4 Active RF splitter an external power supply such as this one is needed to ensure enough power supplied to both splitters

Active RF Splitters are listed at Active RF Splitters.