Most modern aircraft have a 400V 360-800Hz three-phase grid, as this allows thinner (read:lighter) conductors. There are some high voltage DC rails on some plains in the range 270VDC or ±270VDC.
On the usage side for instrumentation, avionics etc. it is usually 28 VDC.
On the usage side for instrumentation, avionics etc. it is usually 28 VDC.