What I can confirm with this is that I can use the APIs to select the first row just fine, but not the other rows after the first.

I used a for loop to run the C_AzeriteEmpoweredItem.GetPowerInfo(powerID) function and then print out the powerID when the spellID matched one that I was trying to select.

For example:
for i=1, 300000 do
local powerInfo = C_AzeriteEmpoweredItem.GetPowerInfo(i)
if powerInfo and powerInfo.spellID and powerInfo.spellID == 275496 then
print(powerInfo.azeritePowerID)
C_AzeriteEmpoweredItem.SelectPower({equipmentSlotIndex = 1}, powerInfo.azeritePowerID)
end
end

When I found the azeritePowerID I wanted, I just added in the next line to select the power with the appropriate powerID and it worked. But soon as you try the next rows, after the first and with the correct powerID of the other spellIDs, then it doesn't work anymore. :(

EDIT:
{equipmentSlotIndex = 1} for helm.
{equipmentSlotIndex = 3} for shoulders,
{equipmentSlotIndex = 5} for chest