PoE injector for FortiAP?

We plan to buy a couple of PoE-capable FortiAP-220B and connect them both to FortiGate-310B. Both units will be installed high on the ceiling without any power around. Because FG-310B does not provide PoE from any of its ports we have to get a couple of PoE injectors to feed FortiAPs. Could anyone recommend a PoE-injector brand/model that works reliably with PoE-capable FortiAP? We don' t want to buy just " anything from the street" and then discover that it doesn' t work to our expectation. Thank you, V.A.