There is a misleading fact on watt on the PSU, current system mostly depends
on the amp on the 12V rail. Therefore a high watt doesn't mean a high 12V
amp.

Since you bought a second hand antec, Antec is a branded PSU and should be
having a high 12V amp, it is possible that the old PSU is starting to get
weak when you bought it. Cards, CPU, HD, maybe second hand, but no to
second hand PSU.

Use a PSU calculator and see how many your system consume power and find a
high 12V amp PSU matching to the watt given by the calculator. You should
find a PSU around 26A and above.