Upgrading an OEM system, an acer TG-885 with an i5-8400 in it, and I have a 400w 80+ PSU with a 300W rating on the 12v rails (18 and 16A I think) It's probably a pseudo multi rail but who knows. Tried putting an RX 570 in it, and while I've had no stability issues, the wattmeter had a maximum of 355W from the wall using furmark+ cpu burner, so assuming 80% that's 284W, I probably should find something a little beefier then? opinions are welcome. I have a line on an Antec PSU with a 360W 12v rail, and since the outervision PSU calc wants ~ a 407W psu it might be a better idea before the blue smoke that powers computers leaks out.