I believe the ER-X is just passthrough, so if you don't have a PoE source, the ER-X can't power anything?
It could if you plug it into a power adapter, given that you don't have PoE in that case. You'd just use the PoE out if that were the case.
Either requires PoE source or power adapter. But it should still be able to power a device, with a power adapter, but without a PoE source to "pass through".