Switched mode PSU DC voltage and current

[MisterMoseley]

Morning all
I’ve posted this elsewhere but no responses so far, so thought someone on AOS may know/be able to help.
19v DC switched mode power supply (brick) is connected through a power meter to the mains.
It’s powering a Raspberry Pi and HAT.
At the mains end, the power meter is showing constant amperage of around 0.05 amps.
Is it a simple mathematical calculation to establish how many amps the Pi/HAT are a actually pulling from the 19v DC brick?
Reason for asking is that recommended 19v PSU for this combo is 3.5 amps but I can’t see that anything like that is needed in real life.
Thanks

[Sherwood]

You're running 19v into a Pi?

[MisterMoseley]

Hi Geoff
Good point and perhaps I should have explained that I have an IQ Audio amp HAT attached to the Pi and the HAT powers the Pi. So my original Pi PSU (5v, 3amps) sits idle.
The amp HAT can be powered by a DC supply ranging from 12 through to 24 volts Dc and the ‘recommended’ supply is 19v with a max of 3.5 amps.
Just to test it was working OK, I have a 19v supply for a JBL speaker. This is the PSU I’m referring to above and at the mains end - where the meter is plugged in, it’s showing 0.05amp max draw from the main.
I just wondered if it would be a case of a simple mathematical calculation;
240/19 * 0.05 - giving 0.6 amps power being drawn by the Pi and HAT (from the 19v brick).
If this is the case, then I do have a spare PSU in the cupboard (rated at 1.5 amps) which would save me spending £25 odd on the ‘recommended’ supply.
Not penny pinching but just don’t want to waste money.
Thanks
Stuart