USB-C might work. USB PD supports 5a at up to 20v, looks like there's also a higher power 50v 5a spec coming up. But if you're using custom PCBs on both ends you don't really care about the PD specification, as long as you're using good quality cables you can treat the connector/cable as a dumb wire that supports sending 5 amps down a few pins. The data lines may also be useful for sending back data from the emitter module, if you had any need for that.
Desktop computers use the Molex Mini-Fit Jr connector for ATX and PCIe power connectors. 6-pin PCIe power cables should be easy to source on the market, you wouldn't need to get custom cables manufactured. Those can carry ~150w. Might also be possible to cheaply source cables with just a 2 or 4 pin connector?
USB-C might work. USB PD supports 5a at up to 20v, looks like there's also a higher power 50v 5a spec coming up. But if you're using custom PCBs on both ends you don't really care about the PD specification, as long as you're using good quality cables you can treat the connector/cable as a dumb wire that supports sending 5 amps down a few pins. The data lines may also be useful for sending back data from the emitter module, if you had any need for that.
Desktop computers use the Molex Mini-Fit Jr connector for ATX and PCIe power connectors. 6-pin PCIe power cables should be easy to source on the market, you wouldn't need to get custom cables manufactured. Those can carry ~150w. Might also be possible to cheaply source cables with just a 2 or 4 pin connector?